This expands the current shadow-banning feature to be usable via
the admin API and adds documentation for it.

A shadow-banned users receives successful responses to their
client-server API requests, but the events are not propagated into rooms.

Shadow-banning a user should be used as a tool of last resort and may lead
to confusing or broken behaviour for the client.

This only applies if the user's data is to be erased.

For remote users, only the rooms which the server knows about are returned.
Local users have all of their joined rooms returned.

These are now only available via `/_synapse/admin/v1`.

Signed-off-by: Chagai Friedlander <chagai95@gmail.com>

Add an admin API `GET /_synapse/admin/v1/users/<user_id>/pushers` like https://matrix.org/docs/spec/client_server/latest#get-matrix-client-r0-pushers

Add admin API `GET /_synapse/admin/v1/users/<user_id>/media` to get information of users' uploaded files.

Add a new admin API `GET /_synapse/admin/v1/users/<user_id>/joined_rooms` to
list all rooms where a user is a member.

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>

* 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

I haven't (yet) documented all of the user-list APIs introduced in
https://github.com/matrix-org/synapse/pull/1784 because the API shape seems
very odd, given the functionality.