[lib] implement changing DM threads settings

Summary:
ENG-8979;

Because we can just return empty ChangeThreadSettingsPayload we were able to update this here, not in each component. This simplified things a lot, implicitly handled loading status, and saved a lot of other work.

To fully support avatars I created ENG-9102.

Test Plan:
Test:

1. Changing thread name
2. Changing thread description
3. Changing thread colors
4. Changing thread avatars (only emojis)

Reviewers: tomek, inka

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D13192