Add accept/decline step to appointing a user as a moderator or admin

[SleeplessOne1917]

Requirements

• Is this a feature request? For questions or discussions use https://lemmy.ml/c/lemmy_support
• Did you check to see if this issue already exists?
• Is this only a feature request? Do not put multiple feature requests in one issue.
• Is this a backend issue? Use the lemmy-ui repo for UI / frontend issues.
• Do you agree to follow the rules in our Code of Conduct?

Is your proposal related to a problem?

Currently, people can be appointed as mods or admins without their consent. This could cause issues if a community or instance gets in some kind of trouble and mods/admins try to shift and dilute blame.

Describe the solution you'd like.

Add a step to mod an admin appointments that allow users to accept or decline an appointment.

Describe alternatives you've considered.

n/a

Additional context

No response

[dullbananas]

Duplucate of #785