[web] introduce TagFarcasterChannelModal

Summary: This diff introduces the TagFarcasterChannelModal component. This modal will show the selected farcaster channel if there is one tag otherwise it will let the user create a tag. Subsequent diffs in this stack will extend this modal

Test Plan:
Please see the screenshot below

w/ tagged channel

w/o tagged channel

Reviewers: kamil, inka, ashoat

Reviewed By: inka, ashoat

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D12530