[web] update EditThreadAvatarMenu to add farcaster option

Summary:
this lets a user set a farcaster thread avatar if the thread belongs to a community tagged with a farcaster channel

Depends on D13749

Test Plan:
successfully set a farcaster avatar in community root thread and child threads. was able to unset the avatar as well.

menu icon looks the same as in the user avatar menu

Reviewers: ashoat

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D13752