https://linear.app/comm/issue/ENG-9509/accepting-a-friend-request-on-web-creates-thin-thread

Related discussion: https://phab.comm.dev/D13940#389316
Now we're throwing an error just in useUpdateRelationships(), there are no changes in getUserIdentities()
and useUsersSupportThickThreads() returns Map instead of Set

Depends on D14022

Throw some error in fetchUserIdentitiesPromise() so that finding user indentity always fails
Mobile user goes to profile -> Friend list and adds the web user as a friend
Before a thin thread was created. Now mobile user sees an alert, because there is no auxUserInfo, no thick thread and call to identity server fails.