feat: add readyz for user informer sync

[ricardomaraschini]

the oauth api server should remain unready until the user and groups have been sync.

[openshift-ci]

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This pull-request has been approved by: ricardomaraschini
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[ricardomaraschini]

/test all

[ricardomaraschini]

/retest

[openshift-ci]

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