Add metrics of RunnerDeployment and HRA

[int128]

I'd like to monitor the metrics of RunnerDeployment and HorizontalRunnerAutoscaler.

This PR includes the following metrics:

• horizontal_runner_autoscaler_min_replicas
• horizontal_runner_autoscaler_max_replicas
• horizontal_runner_autoscaler_desired_replicas
• runner_deployment_replicas

Related to #312.

[mumoshu]

Perhaps it would be a bit better to use names that are similar to those of kube-state-metrics? In kube-state-metrics, the namespace label is just namespace regardless of the kind and the name label is the lowercase kind name:

Suggested change

	rdName = "rd_name"
	rdNamespace = "rd_namespace"
	rdName = "runnerdeployment"
	rdNamespace = "namespace"

[int128]

Good point 👍
I changed the labels to kube-state-metrics style. It would be better for consistency between various components such as kube-state-metrics.

[mumoshu]

Sorry for the back-and-forth but according to how kube-state-metrics using horizontalpodautocaler instead of horizontal_pod_autoscaler, this could:

Suggested change

	Name: "horizontal_runner_autoscaler_min_replicas",
	Name: "horizontalrunnerautoscaler_min_replicas",

[int128]

Exactly. I changed the name to horizontalrunnerautoscaler_spec_min_replicas like kube-state-metrics.

[mumoshu]

Similarly, this could be:

Suggested change

	Name: "runner_deployment_replicas",
	Name: "runnerdeployment_replicas",

[mumoshu]

LGTM 👍 Thanks for your support @int128 ☺️