[native] implement onPressTagChannel for TagUnfollowedFarcasterChannel

Summary:
This diff implements the logic for onPressTagChannel in TagUnfollowedFarcasterChannel. The important thing about this method is that before dispatching our action promise, we want to validate the input through fetchFarcasterChannelByName

Depends on D11857

Test Plan: Confirmed that fetchFarcasterChannelByName correctly validates the input and createOrUpdateFarcasterChannelTag action is dispatched when the input is valid. Otherwise confirmed that I was logging the error message

Reviewers: inka, ashoat

Reviewed By: ashoat

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D11866