Share cluster: Set up oidc groups-claim

[alvaroaleman]

What this PR does / why we need it:

Sets the oidc groups claim when the share cluster feature is enabled, so groups can be used for permission management.

I've tested that this does't cause issues when the IDP does not set the groups property

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:

Documentation:

Does this PR introduce a user-facing change?:

The share cluster feature now allows to use groups, if passed by the IDP. All groups are prefixed with `oidc:`

/assign @thz @zreigz

[thz]

/lgtm
/approve

[kubermatic-bot]

LGTM label has been added.

Git tree hash: 4a3de3c5acbfdf76022ee8369bab1c41e02c2361

[kubermatic-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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