Export Prometheus Metrics

[Dentrax]

Is your feature request related to a problem? Please describe.

Need to monitor the Pinniped supervisor(s) and concierge(s).

Describe the solution you'd like

Define and export some important Prometheus metrics.

Describe alternatives you've considered

Expose and monitor OIDCIdentityProvider's .status field via kube-state-metrics using CustomResourceState metrics.

Are you considering submitting a PR for this feature?

Might be, in the future, but can't make any promises.

• How will this project improvement be tested?

Jump to /metrics, check if its 200, and validate with promtool check tool.

• How does this change the current architecture?

Zero change needed.

• How will this change be backwards compatible?

Not a breaking change.

• How will this feature be documented?

Define each metric' name and description.

Additional context

• https://prometheus.io/docs/guides/go-application/
• https://github.com/prometheus/client_golang