feat: add support for identity service in GCPManagedControlPlane

[afarbos]

What type of PR is this?

/kind feature

What this PR does / why we need it:

The goal of this PR is to add identity service support, see https://cloud.google.com/kubernetes-engine/docs/how-to/oidc
This kind of feature enabled use of OIDC

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

Special notes for your reviewer: how can I run test locally?

Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

TODOs:

• squashed commits
• includes documentation
• adds unit tests

Release note:

Add support for identity service on GKE control plane 

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[afarbos]

make verify & make test pass locally

[cpanato]

/ok-to-test

[salasberryfin]

Thanks @afarbos, could you also add a release note to the PR's description?

[afarbos]

Thanks @afarbos, could you also add a release note to the PR's description?

done!

[salasberryfin]

Thanks @afarbos

/lgtm

[cpanato]

/kind feature
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: afarbos, cpanato

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• OWNERS [cpanato]

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