[landing] introduce ConnectFarcaster

Summary:
introduce ConnectFarcaster component. This component should return null as the purpose of this component is to call the useSignIn hook from @farcaster/auth-kit and return it to the react native webview component (introduced in subsequent diffs)

Depends on D11427

Test Plan: Confirmed that I was able to get both the farcaster_url and the farcaster_data back in the native message webview whenever this component was rendered in the native webview component + tested the entire sign in flow during the hackathon

Reviewers: atul

Reviewed By: atul

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D11428