Add create/edit/delete beatmap discussion post API endpoints

[Hiviexd]

some cool uses for this would be:

• NAT bot automatically posting veto conclusions
• a bot that automatically posts detected unrankables in a given beatmap

[minetoblend]

I'm currently trying to integrate beatmap discussions into osucad and want to add the ability to create beatmap discussion posts from within the editor (see video below), for which I would need these endpoints.

I am interested in contributing this feature myself, but I don't want to just PR this out of the blue without any prior discussion.
Is a contribution that would be accepted? Additionally, I want to ask what the oauth scope required for this would look like. My current idea is a beatmapset_discussion.write scope which would behave just like the forum.write scope.

2024-03-01.03-21-23.mp4