Document bulk ban endpoint

[MinnDevelopment]

This endpoint has some interesting pitfalls when a user is not banned.

• If a user was already banned, they are in the "failed_users" array
• If you don't have permissions to ban a user, they also appear in failed users
• If all users "failed" you get an error response instead
• The endpoint filters out the self user (does not show up in either array)

[NeloBlivion]

Is this endpoint working as intended? Used it to ban 150 users, one was already banned so it comes down to 149 successful, 1 failed. However, i still got 500000 Failed to ban users instead of the two arrays.
In another server where all bans were successful, it worked as intended.