🌱 Allow control plane provider to set endpoint

[vincepri]

What this PR does / why we need it:
/area api

This small change allows the controlPlaneRef, if set, to conditionally set the controlPlaneEndpoint. This change is a short term solution that allows the control plane provider to be on parity with the infrastructure provider, and helps reduce the heavy requirement on the infrastructureRef we have today.

Eventually, once the ClusterEndpoint proposal is implemented, those endpoints will superseded this change.

[fabriziopandini]

Thanks for this PR!

Eventually, once the ClusterEndpoint proposal is implemented, those endpoints will superseded this change.

What about adding a note on top of https://github.com/kubernetes-sigs/cluster-api/blob/main/docs/proposals/20230407-flexible-managed-k8s-endpoints.md so we keep track we have implemented this / it should be considered when someone pick up
the implementation

I also think we should fix documentation in:

• https://cluster-api.sigs.k8s.io/developer/architecture/controllers/control-plane#relationship-to-other-cluster-api-types (it is not true anymore that controlPlane providers have to wait for controlPlaneEndpoint, it depends now...)
• https://cluster-api.sigs.k8s.io/developer/architecture/controllers/control-plane#crd-contracts (we should add the controlPlane endpoint as optional)

[vincepri]

@fabriziopandini done, ptal

[fabriziopandini]

One last nit.
If possible, please add a note in https://cluster-api.sigs.k8s.io/developer/architecture/controllers/cluster#infrastructure-provider indicating that the control plane endpoint might be not provided by the infrastructure cluster (sorry if I forgot to list this page in the first pass)

[enxebre]

The change seems reasonable to me.

[vincepri]

@sbueringer & others, ptal

[enxebre]

/lgtm

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: d6f31e3d259613f74ca4b67474655243b96724e9

[chrischdi]

/approve

Besides the naming nit

/hold in case @sbueringer or others want to take a look too.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: chrischdi

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wrong button

[enxebre]

/lgtm

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 26cb7a5167caecaf21b06da10ceca36bf64c3990

[vincepri]

/hold cancel

[vincepri]

@sbueringer @enxebre ready for another review

[enxebre]

/lgtm
/hold
in case Stefan wants to have another look

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: dba32f9fff1ebb273d4fe2b0463a6dfedb3c6356

[fabriziopandini]

/lgtm

[vincepri]

/hold cancel

[sbueringer]

/lgtm

from my side as well

[vincepri]

/cherry-pick release-1.7

[k8s-infra-cherrypick-robot]

@vincepri: #10667 failed to apply on top of branch "release-1.7":

Applying: Allow control plane provider to set endpoint
Using index info to reconstruct a base tree...
M	docs/book/src/developer/architecture/controllers/cluster.md
M	docs/book/src/developer/architecture/controllers/control-plane.md
M	internal/controllers/cluster/cluster_controller_phases.go
M	internal/controllers/cluster/cluster_controller_phases_test.go
Falling back to patching base and 3-way merge...
Auto-merging internal/controllers/cluster/cluster_controller_phases_test.go
Auto-merging internal/controllers/cluster/cluster_controller_phases.go
Auto-merging docs/book/src/developer/architecture/controllers/control-plane.md
Auto-merging docs/book/src/developer/architecture/controllers/cluster.md
CONFLICT (content): Merge conflict in docs/book/src/developer/architecture/controllers/cluster.md
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
Patch failed at 0001 Allow control plane provider to set endpoint
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".

In response to this:

/cherry-pick release-1.7

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