[lib] introduce DISABLE_CONNECT_FARCASTER_ALERT gate

Summary: Since we plan on flipping usingCommServicesAccessToken to true for devs we need to create a new gate for the connect farcaster prompt

Test Plan: flow + confirmed that the gate works as expected

Reviewers: varun, ashoat

Reviewed By: ashoat

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D12473