postgres: databroker storage backend (#3370)

* wip

* storage: add filtering to SyncLatest

* don't increment the record version, so intermediate changes are requested

* databroker: add support for query filtering

* fill server and record version

* postgres: databroker storage backend

* wip

* serialize puts

* add test

* skip tests for macos

* add test

* return error from protojson

* set data

* exclude postgres from cover tests

pkg/storage/postgres/option.go

@@ -0,0 +1,30 @@
+package postgres
+
+import (
+	"time"
+)
+
+const defaultExpiry = time.Hour * 24
+
+type config struct {
+	expiry time.Duration
+}
+
+// Option customizes a Backend.
+type Option func(*config)
+
+// WithExpiry sets the expiry for changes.
+func WithExpiry(expiry time.Duration) Option {
+	return func(cfg *config) {
+		cfg.expiry = expiry
+	}
+}
+
+func getConfig(options ...Option) *config {
+	cfg := new(config)
+	WithExpiry(defaultExpiry)(cfg)
+	for _, o := range options {
+		o(cfg)
+	}
+	return cfg
+}