* Add get-sub-conversation endpoint type
* Refactor: Generalize getConversationAndCheckMembership
* Add federation and generalize client endpoint
* Int. test: local member, remote subconversation
* Fix bug: conversation qualified wrong
* Add tests for federation endpoint
* Move test stub into correct group
* Add changelog entry
* Remove unused constraints

Co-authored-by: Marko Dimjašević <[email protected]>