* Fix membership state table and diagram
There were 2 missing cases which are legal:
* `invite->knock` (a fairly silly thing to do, but legal under the auth rules)
* `external->leave (via /kick)` (another somewhat silly thing to do, but no different than `external->ban (via /ban)`)
The state table considered the first as illegal, which is untrue.
* Changelog
* Make the graph prettier
* Update changelogs/client_server/newsfragments/3730.clarification
Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
