[lib] Update union types in message-types to include UpdateRelationship types

Summary:
Basically mirrored where the types in legacy-update-relationships were being consumed.

Based on following from hackathon branch: https://github.com/CommE2E/comm/commit/d11c46cfbc61c67e4719c419e393c1b80d0130c4

Depends on D11438

Test Plan: flow/things work as expected

Reviewers: varun, tomek, ginsu, will

Reviewed By: ginsu

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D11439