[native] render thread avatar in CHANNEL AVATAR thread settings section

Summary:
Introduce CHANNEL AVATAR section in thread settings and render thread avatar in this new section

Depends on D7134

Test Plan:
Please take a look at the screenshots to see the changes I made:

staff user:

non staff user:

Reviewers: ashoat, atul

Reviewed By: ashoat

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D7135