✨ Add annotations to ClusterClass variables

[Danil-Grigorev]

What this PR does / why we need it:
Adding field for storing arbitrary metadata as annotations to a cluster class variable.

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 #10023

/area clusterclass

[k8s-ci-robot]

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[Danil-Grigorev]

/area clusterclass

[sbueringer]

/hold

to continue the discussion on the issue first (I don't want to split the discussion between issue & PR)

[sbueringer]

/close

in favor of #10308

[k8s-ci-robot]

@sbueringer: Closed this PR.

In response to this:

/close

in favor of #10308

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