Make it clear (in both ban command and propagation protection) when banning if the target user has already been banned

[Gnuxie]

Currently if the target user is already banned, the propagation prompts will do nothing. And the ban command will also quit with a green tick. This can make a user believe that the bot is silently failing. When the reality is that the target user was banned all along.

Context:https://matrix.to/#/!IaWNErZAgQUhGqJXjX:matrix.org/$wo4uiqHXF1wiqkz7o-Y1lOgNv3l3GhAi3L-swE1Av30?via=matrix.org&via=envs.net&via=ubuntu.com

It's quite a major problem because it managed to lead us to believe that there could a problem in the entire stack (inclusive of homeserver) where users with unusual mxids can ban evade. And start plotting a response.