Add server-wide and user-only federation controls (#133)

### Description

Completes #122

### Please confirm

- [x] I am the legal owner or represent the legal owner of all work submitted (including LLM-generated code, if any)
- [x] I consent to my changes being added to this FOSS project
- [x] I have confirmed that this does not add new errors or warnings with `utils/clippy.sh`
- [ ] This PR used LLMs to generate some or all of the code changes

Reviewed-on: https://git.ngram.ca/OpenJam/rc-servers/pulls/133

rc_database/src/schema/user_aux.rs

@@ -44,4 +44,5 @@ pub enum Descriptor {
     SubscribedChannels, // Vec<String>, JSON
     AvatarId, // u32, u32::MAX means custom avatar
     RedeemedPromoCodes, // Vec<String>, JSON
+    Federation, // oj_rc_Core::persist::user::Federation, JSON
 }