chore: test metricscache on postgres (#16711)

metricscache_test has been running tests against dbmem only, instead of
against postgres. Unfortunately the implementations of
GetTemplateAverageBuildTime have diverged between dbmem and postgres.
This change gets the tests working on Postgres and test for the
behaviour postgres provides.

coderd/coderd.go

@@ -422,6 +422,7 @@ func New(options *Options) *API {
 	metricsCache := metricscache.New(
 		options.Database,
 		options.Logger.Named("metrics_cache"),
+		options.Clock,
 		metricscache.Intervals{
 			TemplateBuildTimes: options.MetricsCacheRefreshInterval,
 			DeploymentStats:    options.AgentStatsRefreshInterval,