feat: align GCPManagedControlPlane with CAPI >=v1.9

[salasberryfin]

/kind bug

What this PR does / why we need it:

To align GCPManagedControlPlane specification and status with CAPI >=v1.9 we need to introduce new control plane version fields and set existing ones for deprecation in coming releases. The list of changes, as agreed on Slack (thanks @damdo @richardcase @cpanato):

• Introduce new Version fields in GCPManagedControlPlaneSpec and GCPManagedControlPlaneStatus as per the updated CAPI contract for control planes.
• Mark ControlPlaneVersion and CurrentVersion as deprecated with a message saying to use Version instead.
• Have a validation webhook that disallows setting Version and ControlPlaneVersion.
• Update all templates and e2e tests to use Version.

Which issue(s) this PR fixes:
Fixes #1433

Special notes for your reviewer:

In the future, as the deprecated field is ultimately removed, we can add a conversion from ControlPlaneVersion to Version.

TODOs:

• squashed commits
• includes documentation
• adds unit tests

Release note:

action required
!! ACTION REQUIRED BEFORE UPGRADING !!
If you are using the GCPManagedControlPlane to provision GKE clusters and you do not have a spec.Version specified in such resource (or you are using spec.ControlPlaneVersion), you will need to either:
a) explicitly set such `spec.Version` field before upgrading CAPG (if you are already using spec.ControlPlaneVersion, please, use spec.Version instead)
or b) disable the MachineSetPreflightChecks in your cluster either:
b1) by setting this core CAPI feature gate to `false`
b2) or by disabling it via the relevant annotation on all the machineSets belonging to said cluster (follow this guide on how to do this: https://cluster-api.sigs.k8s.io/tasks/experimental-features/machineset-preflight-checks).
This is necessary as core CAPI 1.9 introduces a feature gate change, setting MachineSetPreflightChecks=true, which in turn relies on the presence of spec.Version and status.Version on the GCPManagedControlPlane object.
These fields will be deprecated in a future release.

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[damdo]

Hey @salasberryfin
Thanks a lot for working on implementing this!

Mostly LGTM, left a couple of things we need to change though.

[damdo]

@salasberryfin Also we will likely need to add an action required in the release-note for this PR,
similar to the one I added for CAPA here: kubernetes-sigs/cluster-api-provider-aws#5209 (comment)
(you should be able to mostly copy-paste it).

cc. @richardcase

[damdo]

@salasberryfin also we might need to silence the linter for errors like : cloud/services/container/clusters/reconcile.go:515:5: SA1019: spec.ControlPlaneVersion is deprecated: This field will soon be removed and you are expected to use Version instead. (staticcheck), as we still want to set/get those fields internally even if they are deprecated, until we remove them.

[richardcase]

Great work @salasberryfin 🎉

Just a couple of minor comments.

[salasberryfin]

Thanks for the reviews @damdo @richardcase. Sorry I couldn't address your comments before, I'll be doing so today!

[damdo]

No worries, thanks @salasberryfin

[salasberryfin]

I think the latest commit addresses all of the comments @damdo @richardcase.

[cpanato]

@salasberryfin there are a few lints to tackle, thanks for working on this

[salasberryfin]

Thanks @cpanato. The exclude rule I added covered some of the cases where the linter found errors but missed some of them. Should be fixed now.

[cpanato]

can be this updated?

[salasberryfin]

I'll update this in a separate PR, if that's okay.

[cpanato]

yes

[salasberryfin]

Also added the action required to the release note. Thanks @damdo!

[alexander-demicev]

/lgtm

[cpanato]

thanks!

/approve

/hold for @richardcase @damdo

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: alexander-demicev, cpanato, salasberryfin

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[damdo]

@salasberryfin Mostly LGTM, I left one blocking question though. LMK thanks!

[salasberryfin]

Thanks for the reviews. The webhook now returns a warning if only spec.controlPlaneVersion is used and an error if both spec.controlPlaneVersion and spec.Version are set. New tests have been added to verify the validation webhook on these scenarios.

[damdo]

Hm looks like the E2Es failed https://prow.k8s.io/view/gs/kubernetes-ci-logs/pr-logs/pull/kubernetes-sigs_cluster-api-provider-gcp/1434/pull-cluster-api-provider-gcp-e2e-test/1897214121795915776

Let's retest for good measure in case it is a flake, otherwise we might need to look into it.

/retest

[salasberryfin]

Thanks @damdo, looks like it was a flake.

[damdo]

/lgtm

Thanks @salasberryfin for working on this

/unhold

[richardcase]

Great work @salasberryfin 🥇