IAM: Enable adding a User to a Group

[samox73]

Is your feature request related to a problem?
Afaict, there is no way to add a user to a group via ACK IAM resources.

Describe the solution you'd like
Add a groupRefs field to the spec of the User CRD similar to policyRefs, so that multiple groups can be attached to a user directly linking to Group CRs.

Describe alternatives you've considered
External/manual management of adding users to groups seems troublesome.

[ack-bot]

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/lifecycle stale

[Alwin-Stockinger]

/remove-lifecycle stale