telemetry: add tracing

- telemetry/tace: add traces throughout code
- telemetry/metrics: nest metrics and trace under telemetry
- telemetry/tace: add service name span to HTTPMetricsHandler.
- telemetry/metrics: removed chain dependency middleware_tests.
- telemetry/metrics: wrap and encapsulate variatic view registration.
- telemetry/tace: add jaeger support for tracing.
- cmd/pomerium: move `parseOptions` to internal/config.
- cmd/pomerium: offload server handling to httputil and sub pkgs.
- httputil: standardize creation/shutdown of http listeners.
- httputil: prefer curve X25519 to P256 when negotiating TLS.
- fileutil: use standardized Getw

Signed-off-by: Bobby DeSimone <bobbydesimone@gmail.com>

internal/fileutil/fileutil.go

@@ -30,3 +30,17 @@ func IsReadableFile(path string) (bool, error) {
 	fd.Close()
 	return true, nil // Item exists and is readable.
 }
+
+// Getwd returns a rooted path name corresponding to the
+// current directory. If the current directory can be
+// reached via multiple paths (due to symbolic links),
+// Getwd may return any one of them.
+//
+// On failure, will return "."
+func Getwd() string {
+	p, err := os.Getwd()
+	if err != nil {
+		return "."
+	}
+	return p
+}