Support upgrading existing test guilds with botstrap #3418
Description
I have a test guild that hasn't been updated recently. I understand that while I'm probably an outlier, it would be nice to be able to upgrade existing test guilds, if sir-lancebot, sir robin, or bot gets an update that requires a new channel or role that doesn't exist in the user guild.
This would need to be opt-in, in order to not delete channels or roles or webhooks the user has created for a different reason. It should have options to upgrade the server and ask on every delete, or approve all deletions.
I propose making a small cli in botstrap using argparse to maintain the current behaviour with no command, but to add an upgrade command which will allow the user to upgrade the server to be in sync with the server template.
This is independent to #3414. If approved, I can optionally implement it into #3417.