Include user tag in ban revoke log message

[danthe1st]

Is your feature request related to a problem? Please describe.
Currently, the Ban revoked log embed only contains a timestamp, the responsible moderator and the id of the unbanned user. It is hard to easily identify users by id.

Describe the solution you'd like
When revoking a ban, the bot should obtain the user with retrieveUserById. If this operation is successful, it should add a field with the tag (username and discriminator) to the ban revoked embed. If the user cannot be obtained, the log message should still be sent but the tag should be ommitted.

It might also be a good idea to include a reason argument/field for unbans.

Describe alternatives you've considered
Using the audit log for this. However, this is tedious.

Additional context