[native] let user choose farcaster avatar

Summary:
This diff makes it possible for a new user to select a farcaster avatar during registration if they have connected their farcaster account. it also makes it possible for existing users to set the farcaster avatar from the profile tab if there's a connected farcaster account.

Depends on D13100

Test Plan: tested at the end of the stack by successfully selecting farcaster avatar during registration. avatar is displayed immediately upon selection and appears in profile after registration is complete

Reviewers: ashoat, tomek

Reviewed By: ashoat

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D13101