[identity] unlink farcaster account RPC
Summary:
- new RPC defined in auth.proto file
- identity service implementation
- db client method to remove the farcasterID attribute from DDB
- grpc-web codegen updates
Depends on D11413
Test Plan:
- added a farcaster ID to a user with the link RPC
- confirmed the ID appeared in DDB
- called the unlink RPC
- confirmed the ID no longer appeared in DDB
- called the unlink RPC again and it succeeded, but nothing changed in DDB, as expected
Reviewers: bartek, ashoat
Reviewed By: bartek, ashoat
Subscribers: tomek
Differential Revision: https://phab.comm.dev/D11423