[lib] Re-introduce RelationshipRequest and replace TraditionalRelationshipRequest where simple

Summary:
Re-introduce RelationshipRequest as union of TraditionalRelationshipRequest|FarcasterRelationship and replace TraditionalRelationshipRequest where simple.

Next steps are to

1. Narrow TraditionalRelationshipRequest so it excludes farcaster action
2. Update FarcasterRelationshipRequest callsite
3. Make necessary changes on keyserver to accomodate

Depends on D11603

Test Plan: flow

Reviewers: varun, ginsu, will, tomek

Reviewed By: ginsu

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D11605