refactor: improved prometheus metrics (#1830)

This will add new prometheus metrics for Kratos that are more useful for alerting and increase overall observability.

BREAKING CHANGES: This patch changes the naming and number of prometheus metrics (see: ory/x#379). In short: all metrics will have now `http_` prefix to conform to Prometheus best practices.

Closes #1735

driver/registry_default.go

@@ -638,7 +638,7 @@ func (m *RegistryDefault) PrometheusManager() *prometheus.MetricsManager {
 	m.rwl.Lock()
 	defer m.rwl.Unlock()
 	if m.pmm == nil {
-		m.pmm = prometheus.NewMetricsManager("kratos", m.buildVersion, m.buildHash, m.buildDate)
+		m.pmm = prometheus.NewMetricsManagerWithPrefix("kratos", prometheus.HTTPMetrics, m.buildVersion, m.buildHash, m.buildDate)
 	}
 	return m.pmm
 }