feat: add prometheus metrics to database.Store (#7713)

* Adds dbmetrics package and wraps database.Store with a Prometheus HistogramVec of timings.
* Adds Wrappers method to database.Store to avoid double-wrapping interfaces
* Fixes test flake in TestLicensesListFake

coderd/database/db.go

@@ -24,11 +24,20 @@ type Store interface {
 	querier
 	// customQuerier contains custom queries that are not generated.
 	customQuerier
+	// wrapper allows us to detect if the interface has been wrapped.
+	wrapper
 
 	Ping(ctx context.Context) (time.Duration, error)
 	InTx(func(Store) error, *sql.TxOptions) error
 }
 
+type wrapper interface {
+	// Wrappers returns a list of wrappers that have been applied to the store.
+	// This is used to detect if the store has already wrapped, and avoid
+	// double-wrapping.
+	Wrappers() []string
+}
+
 // DBTX represents a database connection or transaction.
 type DBTX interface {
 	ExecContext(context.Context, string, ...interface{}) (sql.Result, error)
@@ -60,6 +69,10 @@ type sqlQuerier struct {
 	db  DBTX
 }
 
+func (*sqlQuerier) Wrappers() []string {
+	return []string{}
+}
+
 // Ping returns the time it takes to ping the database.
 func (q *sqlQuerier) Ping(ctx context.Context) (time.Duration, error) {
 	start := time.Now()