[web] Create a modal where invite link can be accepted

Summary:
This modal allows accepting the invitation. If a link is invalid, a message is displayed.

Depends on D7949

Test Plan: Tested in combination with next diffs - depending on the validity of a link a different modal should be displayed.

Reviewers: bartek, kamil, inka

Reviewed By: inka

Subscribers: ashoat, atul

Differential Revision: https://phab.comm.dev/D7957