Introduce MR metrics

[ezgidemirel]

Description of your changes

This change introduces MR metrics to provider-helm.

Fixes #

I have:

• Read and followed Crossplane's contribution process.
• Run make reviewable to ensure this PR is ready for review.

How has this code been tested

Deployed the custom image to a cluster and verified the metrics

Ezgis-MacBook-Pro:phase-2 ezgidemirel$ curl -s http://localhost:8080/metrics |grep crossplane_
# HELP crossplane_managed_resource_exists The number of managed resources that exist
# TYPE crossplane_managed_resource_exists gauge
crossplane_managed_resource_exists{gvk="helm.crossplane.io/v1beta1, Kind=Release"} 10
# HELP crossplane_managed_resource_ready The number of managed resources in Ready=True state
# TYPE crossplane_managed_resource_ready gauge
crossplane_managed_resource_ready{gvk="helm.crossplane.io/v1beta1, Kind=Release"} 10
# HELP crossplane_managed_resource_synced The number of managed resources in Synced=True state
# TYPE crossplane_managed_resource_synced gauge
crossplane_managed_resource_synced{gvk="helm.crossplane.io/v1beta1, Kind=Release"} 10

[turkenh]

Thanks @ezgidemirel 🙌