[web] Call join thread endpoint
Clicking join button results in calling server endpoint. Depending on the result either user sees a modal with an error, or a modal is closed.
Depends on D7957
Open invite link, accept the invitation - modal should be closed and the community should appear on the list.
Modify join thread endpoint so that it always throws. Accept the invitation - a message about invalid link should appear.
Reviewers: bartek, kamil, inka
Reviewed By: inka
Subscribers: ashoat, atul
Differential Revision: https://phab.comm.dev/D7958