Support updates to User resources & credential Secrets

[coro]

Is your feature request related to a problem? Please describe.
Currently, User objects can only be created and deleted, but not updated.

Describe the solution you'd like

Editing the User

• Changing User.Spec.Name or User.Spec.RabbitmqClusterReference: TBD, but probably reject the request with a validating webhook, rather than delete the existing user and create a new one. Otherwise, an app consuming the User Secret will have to reload the secret to regain access to an authenticated user.
• Changing User.Spec.Tags: Updates the tags associated with a user.

Editing the User Secret

• Changing Secret.Data["username"]: TBD, but again probably reject the request
• Changing Secret.Data["password"]: Calculate a new password hash and update the user

Additional context
Original Issue: #3

[github-actions]

This issue has been marked as stale due to 60 days of inactivity. Stale issues will be closed after a further 30 days of inactivity; please remove the stale label in order to prevent this occurring.

[github-actions]

Closing stale issue due to further inactivity.

[carlosjgp]

could we reopen this?

[cronventis]

Please implement :)