Add MAS Token Bot plugin

[NataliaWoof]

Adding MAS token bot to the official plugin list for maubot

[williamkray]

hmm, same linting error as #36

@tulir lemme know how you feel about merging anyway or if you prefer devs pass linting first. everything else looks ok to me.

[tulir]

The linters need to pass, pre-commit can run locally or the problems can just be fixed manually (the check says what's wrong, i.e. trim trailing whitespace failing means there's extra trailing whitespace)