[lib] Split UpdateRelationshipMessageInfo into Update[Traditional/Farcaster]RelationshipMessageInfo

Summary:
Similar to previous diffs in stack, splitting the type to support farcaster operation.

Made necessary changes to update-relationship-message-spec as well.

Depends on D11642

Test Plan: Flow for now, will be tested implicitly by subsequent diffs where these messages are actually created/persisted/etc.

Reviewers: ginsu, tomek, varun, will

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D11650