Fixes https://github.com/matrix-org/synapse/issues/8185

Some fixes to wording I noticed after merging #7377.

* Search in columns 'name' and 'displayname' in the admin users endpoint

Signed-off-by: Manuel Stahl <manuel.stahl@awesome-technologies.de>

These docs were tested successfully in production by a customer, so it's probably fine.

Add option ```purge``` to ```POST /_synapse/admin/v1/rooms/<room_id>/delete```
Fixes: #3761

Signed-off-by: Dirk Klimpel <dirk@klimpel.org>

The Delete Room admin API allows server admins to remove rooms from server
and block these rooms.
`DELETE /_synapse/admin/v1/rooms/<room_id>`
It is a combination and improvement of "[Shutdown room](https://github.com/matrix-org/synapse/blob/develop/docs/admin_api/shutdown_room.md)" and "[Purge room](https://github.com/matrix-org/synapse/blob/develop/docs/admin_api/purge_room.md)" API.

Fixes: #6425 

It also fixes a bug in [synapse/storage/data_stores/main/room.py](synapse/storage/data_stores/main/room.py) in ` get_room_with_stats`.
It should return `None` if the room is unknown. But it returns an `IndexError`.
https://github.com/matrix-org/synapse/blob/901b1fa561e3cc661d78aa96d59802cf2078cb0d/synapse/storage/data_stores/main/room.py#L99-L105

Related to:
- #5575
- https://github.com/Awesome-Technologies/synapse-admin/issues/17



Signed-off-by: Dirk Klimpel <dirk@klimpel.org>

* Clarify how to authenticate
* path params are not the same thing as query params
* Fix documentation for `/_synapse/admin/v2/users/<user_id>`

- Admin is able to
  - change displaynames
  - delete devices
  - list devices
  - get device informations

Fixes #7330

Signed-off-by: Manuel Stahl <manuel.stahl@awesome-technologies.de>

Update documentation to reflect the correct format of user_id (fully qualified).

Signed-off-by: Manuel Stahl <manuel.stahl@awesome-technologies.de>

Signed-off-by: Olivier Wilkinson (reivilibre) <olivier@librepush.net>

Admin API: Set adminship of a user

This endpoint isn't much use for its intended purpose if you first need to get
yourself an admin's auth token.

I've restricted it to the `/_synapse/admin` path to make it a bit easier to
lock down for those concerned about exposing this information. I don't imagine
anyone is using it in anger currently.