Remove custom metrics API implementation (keep external metrics)

[astefanutti]

WHY

The multi-cluster mode relies on serving the Kubernetes external metrics API, to provide resource allocation information on the MCAD agent cluster nodes. This is achieved by embedding and copy of the custom-metrics-apiserver, which provides a template to implement both the custom and external metrics APIs. However, the implementation of the custom metrics API is not used at all.

WHAT

Remove the custom metrics API implementation, as well as the corresponding APIService and ClusterRoleBinding resources.

TESTS

The e2e tests should pass.

[asm582]

FYI, @dmatch01 the codeflare operator is disabling the above features for a single cluster install.

[asm582]

Adding @metalcycling to the thread.