[landing] introduce /connect-farcaster route

Summary:
After introducing the ConnectFarcaster component we should implement the necessary routing logic to route to it whenever the url is BASE_LANDING_URL/connect-farcaster

Depends on D11428

Test Plan: Confirmed that I was able to route to BASE_LANDING_URL/connect-farcaster + tested the entire sign in flow during the hackathon

Reviewers: atul

Reviewed By: atul

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D11429