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:

Add new GCPManagedControlPlane Version field and set ControlPlaneVersion for deprecation to align with core CAPI

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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]

I think the optional stylistically (and maybe even from an implementation standpoint) goes next to the field, whereas the Deprecated can also go above in the godoc comment.
Better be safe, example here:
https://github.com/kubernetes-sigs/cluster-api/blob/7a71f4b0ed71cb92fa751e48057df6bb672319bb/api/v1beta1/cluster_types.go#L533-L539

[damdo]

Same here

[damdo]

We want to populate this status.Version with whatever we currently populate the status.CurrentVersion with.
Then When in the future we remove the status.CurrentVersion, we will only have the status.Version to set.

One instance I saw of this is here:

cluster-api-provider-gcp/cloud/services/container/clusters/reconcile.go

Line 99 in d80bfab

s.scope.GCPManagedControlPlane.Status.CurrentVersion = convertToSdkMasterVersion(cluster.GetCurrentMasterVersion())

But there may be others.

[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.