Custom Endpoint Support

[barbacbd]

/kind feature

Describe the solution you'd like
[A clear and concise description of what you want to happen.]
As a user I want to be able to use GCP Restricted and/or Private API endpoints while deploying OpenShift so I can be complaint with my company security policies.

For users with strict regulatory policies, Private Service Connect allows private consumption of services across VPC networks that belong to different groups, teams, projects, or organizations. Supporting these private endpoints is key for these customers to be able to deploy the platform on GCP and be complaint with their regulatory policies.

Anything else you would like to add:
[Miscellaneous information that will assist in solving the issue.]
This will require API changes to allow the users to supply any/all API Endpoint information. This will require a strict structure to manage valid service names. For instance "compute" should be excepted as a key or name of a service but "comp" cannot be accepted. This will probably require extra documentation.

[barbacbd]

/cc @patrickdillon

[barbacbd]

/cc @damdo

[barbacbd]

Would it be better to add something like

ServiceEndpoints map[string]string `json:"serviceEndpoints,omitempty"`

To the cluster spec (and status) or to the Controller?

[damdo]

/assign @richardcase @salasberryfin @cpanato
For reviews

[damdo]

@barbacbd where are the touchpoints in code where these service endpoints will be plugging in (overriding the default I guess)?

[patrickdillon]

It might be worth noting that CAPA passes the aws equivalent endpoints through flags: https://github.com/kubernetes-sigs/cluster-api-provider-aws/blob/main/pkg/cloud/endpoints/endpoints.go

[barbacbd]

@damdo The place where these would actually be set is in this file: https://github.com/kubernetes-sigs/cluster-api-provider-gcp/blob/main/cloud/scope/clients.go.

There is currently an example here: https://github.com/kubernetes-sigs/cluster-api-provider-gcp/blob/main/cloud/scope/clients.go#L151. Similarly, we would need these for any client we create. In this case though we can pass a *string or string. If there is a value set for the endpoint override then we would add that as an opt option when creating the client for that particular service.

[damdo]

Sound a reasonable feature to me.
Happy to review a PR that implements this for CAPG.
Do you agree @cpanato @richardcase @salasberryfin ?