[native] handle loading state in TagFarcasterChannelByName

Summary: As I am working on bringing the channel tagging UI to web, I noticed that I did not properly handle loading states in the TagFarcasterChannelByName screen. We can use the newly introduced useCreateFarcasterChannelTag hook to both fix this omission + simply this component

Test Plan: Confirmed that there is a loading state when attempting to tag a farcaster channel by name

Reviewers: inka, kamil

Reviewed By: inka

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D12541