[native] introduce TagChannelButton

Summary:
Move diff. In subsequent diffs, I plan to introduce other logic + UI elements to the TagFarcasterChannel screen. In preparation for that I wanted to factor out all the tag channel button logic into it's own separate component so that TagFarcasterChannel isn't too crowded

Depends on D12023

Test Plan: flow + confirmed everything still works as expected

Reviewers: tomek, inka

Reviewed By: tomek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D12024