prometheus: Initialize mgmt_checkapply_total metrics

It is recommended by Prometheus to initialize metrics:

https://prometheus.io/docs/practices/instrumentation/#avoid-missing-metrics

This commits initialize the mgmt_checkapply_total metric
for each registered resource.

Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>

resources/resources.go

@@ -52,6 +52,15 @@ func RegisterResource(kind string, fn func() Res) {
 	registeredResources[kind] = fn
 }
 
+// RegisteredResourcesNames returns the kind of the registered resources.
+func RegisteredResourcesNames() []string {
+	kinds := []string{}
+	for k := range registeredResources {
+		kinds = append(kinds, k)
+	}
+	return kinds
+}
+
 // NewResource returns an empty resource object from a registered kind. It
 // errors if the resource kind doesn't exist.
 func NewResource(kind string) (Res, error) {