AdminAPI: let moderators actually do things

Fixes #2490 (closed)

Upstream MR: https://gitlab.com/soapbox-pub/soapbox/-/merge_requests/39

Allows moderators to do the following:

• Manage user tags (force NSFW, etc)
• Activate, deactivate, and approve users
• Delete users
• Manage invites
• List users, view individual users
• View a user's statuses, private messages, and chat messages
• Manage reports
• View the moderation log
• Manage custom emoji
• View instance stats