metrics: don't add units and scope tags to prometheus metrics (#5749)

## Summary

With metrics now going via OTEL -> Prometheus exporter, there were
couple issues:

- some newer metrics had non-standard units that ended up in metric
names like `pomerium_storage_global_cache_hits__hit__total`
- we had three additional tags (`otel_scope_name`,
`otel_scope_schema_url`, `otel_scope_version`) added to each metric,
which do not really carry much meaningful information for us and expand
metric cardinality.

This PR reverts those two changes and updates the prometheus exporter.

## Related issues

Related: https://github.com/open-telemetry/opentelemetry-go/issues/7039

## User Explanation

<!-- How would you explain this change to the user? If this
change doesn't create any user-facing changes, you can leave
this blank. If filled out, add the `docs` label -->

## Checklist

- [x] reference any related issues
- [ ] updated unit tests
- [x] add appropriate label (`enhancement`, `bug`, `breaking`,
`dependencies`, `ci`)
- [x] ready for review

go.mod

@@ -90,7 +90,7 @@ require (
 	go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.37.0
 	go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.37.0
 	go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp v1.37.0
-	go.opentelemetry.io/otel/exporters/prometheus v0.59.0
+	go.opentelemetry.io/otel/exporters/prometheus v0.59.1
 	go.opentelemetry.io/otel/metric v1.37.0
 	go.opentelemetry.io/otel/sdk v1.37.0
 	go.opentelemetry.io/otel/sdk/metric v1.37.0
@@ -103,7 +103,7 @@ require (
 	golang.org/x/net v0.41.0
 	golang.org/x/oauth2 v0.30.0
 	golang.org/x/sync v0.15.0
-	golang.org/x/sys v0.33.0
+	golang.org/x/sys v0.34.0
 	golang.org/x/term v0.32.0
 	golang.org/x/time v0.12.0
 	google.golang.org/api v0.240.0
@@ -197,6 +197,7 @@ require (
 	github.com/googleapis/enterprise-certificate-proxy v0.3.6 // indirect
 	github.com/googleapis/gax-go/v2 v2.14.2 // indirect
 	github.com/gorilla/securecookie v1.1.1 // indirect
+	github.com/grafana/regexp v0.0.0-20240518133315-a468a5bfb3bc // indirect
 	github.com/grpc-ecosystem/grpc-gateway/v2 v2.27.1 // indirect
 	github.com/hashicorp/errwrap v1.1.0 // indirect
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
@@ -240,6 +241,7 @@ require (
 	github.com/planetscale/vtprotobuf v0.6.1-0.20240319094008-0393e58bdf10 // indirect
 	github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 // indirect
 	github.com/power-devops/perfstat v0.0.0-20240221224432-82ca36839d55 // indirect
+	github.com/prometheus/otlptranslator v0.0.0-20250717125610-8549f4ab4f8f // indirect
 	github.com/prometheus/statsd_exporter v0.22.7 // indirect
 	github.com/quic-go/qpack v0.5.1 // indirect
 	github.com/rcrowley/go-metrics v0.0.0-20201227073835-cf1acfcdf475 // indirect

go.sum

@@ -434,6 +434,8 @@ github.com/gorilla/securecookie v1.1.1 h1:miw7JPhV+b/lAHSXz4qd/nN9jRiAFV5FwjeKyC
 github.com/gorilla/securecookie v1.1.1/go.mod h1:ra0sb63/xPlUeL+yeDciTfxMRAA+MP+HVt/4epWDjd4=
 github.com/gorilla/websocket v1.5.3 h1:saDtZ6Pbx/0u+bgYQ3q96pZgCzfhKXGPqt7kZ72aNNg=
 github.com/gorilla/websocket v1.5.3/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=
+github.com/grafana/regexp v0.0.0-20240518133315-a468a5bfb3bc h1:GN2Lv3MGO7AS6PrRoT6yV5+wkrOpcszoIsO4+4ds248=
+github.com/grafana/regexp v0.0.0-20240518133315-a468a5bfb3bc/go.mod h1:+JKpmjMGhpgPL+rXZ5nsZieVzvarn86asRlBg4uNGnk=
 github.com/gregjones/httpcache v0.0.0-20190611155906-901d90724c79 h1:+ngKgrYPPJrOjhax5N+uePQ0Fh1Z7PheYoUI/0nzkPA=
 github.com/gregjones/httpcache v0.0.0-20190611155906-901d90724c79/go.mod h1:FecbI9+v66THATjSRHfNgh1IVFe/9kFxbXtjV0ctIMA=
 github.com/grpc-ecosystem/go-grpc-middleware/v2 v2.3.2 h1:sGm2vDRFUrQJO/Veii4h4zG2vvqG6uWNkBHSTqXOZk0=
@@ -651,6 +653,8 @@ github.com/prometheus/common v0.35.0/go.mod h1:phzohg0JFMnBEFGxTDbfu3QyL5GI8gTQJ
 github.com/prometheus/common v0.37.0/go.mod h1:phzohg0JFMnBEFGxTDbfu3QyL5GI8gTQJFhYO5B3mfA=
 github.com/prometheus/common v0.65.0 h1:QDwzd+G1twt//Kwj/Ww6E9FQq1iVMmODnILtW1t2VzE=
 github.com/prometheus/common v0.65.0/go.mod h1:0gZns+BLRQ3V6NdaerOhMbwwRbNh9hkGINtQAsP5GS8=
+github.com/prometheus/otlptranslator v0.0.0-20250717125610-8549f4ab4f8f h1:QQB6SuvGZjK8kdc2YaLJpYhV8fxauOsjE6jgcL6YJ8Q=
+github.com/prometheus/otlptranslator v0.0.0-20250717125610-8549f4ab4f8f/go.mod h1:P8AwMgdD7XEr6QRUJ2QWLpiAZTgTE2UYgjlu3svompI=
 github.com/prometheus/procfs v0.0.0-20181005140218-185b4288413d/go.mod h1:c3At6R/oaqEKCNdg8wHV1ftS6bRYblBhIjjI8uT2IGk=
 github.com/prometheus/procfs v0.0.2/go.mod h1:TjEm7ze935MbeOT/UhFTIMYKhuLP4wbCsTZCD3I8kEA=
 github.com/prometheus/procfs v0.1.3/go.mod h1:lV6e/gmhEcM9IjHGsFOCxxuZ+z1YqCvr4OA4YeYWdaU=
@@ -832,8 +836,8 @@ go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.37.0 h1:EtFWS
 go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.37.0/go.mod h1:QjUEoiGCPkvFZ/MjK6ZZfNOS6mfVEVKYE99dFhuN2LI=
 go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp v1.37.0 h1:bDMKF3RUSxshZ5OjOTi8rsHGaPKsAt76FaqgvIUySLc=
 go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp v1.37.0/go.mod h1:dDT67G/IkA46Mr2l9Uj7HsQVwsjASyV9SjGofsiUZDA=
-go.opentelemetry.io/otel/exporters/prometheus v0.59.0 h1:HHf+wKS6o5++XZhS98wvILrLVgHxjA/AMjqHKes+uzo=
+go.opentelemetry.io/otel/exporters/prometheus v0.59.1 h1:HcpSkTkJbggT8bjYP+BjyqPWlD17BH9C5CYNKeDzmcA=
-go.opentelemetry.io/otel/exporters/prometheus v0.59.0/go.mod h1:R8GpRXTZrqvXHDEGVH5bF6+JqAZcK8PjJcZ5nGhEWiE=
+go.opentelemetry.io/otel/exporters/prometheus v0.59.1/go.mod h1:0FJL+gjuUoM07xzik3KPBaN+nz/CoB15kV6WLMiXZag=
 go.opentelemetry.io/otel/exporters/stdout/stdoutmetric v1.36.0 h1:rixTyDGXFxRy1xzhKrotaHy3/KXdPhlWARrCgK+eqUY=
 go.opentelemetry.io/otel/exporters/stdout/stdoutmetric v1.36.0/go.mod h1:dowW6UsM9MKbJq5JTz2AMVp3/5iW5I/TStsk8S+CfHw=
 go.opentelemetry.io/otel/metric v1.37.0 h1:mvwbQS5m0tbmqML4NqK+e3aDiO02vsf/WgbsdpcPoZE=
@@ -1032,8 +1036,8 @@ golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.8.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.12.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.17.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
-golang.org/x/sys v0.33.0 h1:q3i8TbbEz+JRD9ywIRlyRAQbM0qF7hu24q3teo2hbuw=
+golang.org/x/sys v0.34.0 h1:H5Y5sJ2L2JRdyv7ROF1he/lPdvFsd0mJHFw2ThKHxLA=
-golang.org/x/sys v0.33.0/go.mod h1:BJP2sWEmIv4KK5OTEluFJCKSidICx8ciO85XgH3Ak8k=
+golang.org/x/sys v0.34.0/go.mod h1:BJP2sWEmIv4KK5OTEluFJCKSidICx8ciO85XgH3Ak8k=
 golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
 golang.org/x/term v0.0.0-20210927222741-03fcf44c2211/go.mod h1:jbD1KX2456YbFQfuXm/mYQcufACuNUgVhRMnK/tPxf8=
 golang.org/x/term v0.5.0/go.mod h1:jMB1sMXY+tzblOD4FWmEbocvup2/aLOaQEp7JmGp78k=

internal/telemetry/metrics/otel.go

@@ -11,7 +11,11 @@ import (
 var Meter metric.Meter
 
 func init() {
-	e, err := prometheus.New(prometheus.WithNamespace("pomerium"))
+	e, err := prometheus.New(
+		prometheus.WithNamespace("pomerium"),
+		prometheus.WithoutUnits(),
+		prometheus.WithoutScopeInfo(),
+	)
 	if err != nil {
 		panic(err)
 	}