Document Shutdown Room admin API (#6541)

changelog.d/6541.doc

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+Document the Room Shutdown Admin API.

docs/admin_api/shutdown_room.md

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+# Shutdown room API
+
+Shuts down a room, preventing new joins and moves local users and room aliases automatically
+to a new room. The new room will be created with the user specified by the
+`new_room_user_id` parameter as room administrator and will contain a message
+explaining what happened. Users invited to the new room will have power level
+-10 by default, and thus be unable to speak. The old room's power levels will be changed to
+disallow any further invites or joins.
+
+The local server will only have the power to move local user and room aliases to
+the new room. Users on other servers will be unaffected.
+
+## API
+
+You will need to authenticate with an access token for an admin user.
+
+### URL
+
+`POST /_synapse/admin/v1/shutdown_room/{room_id}`
+
+### URL Parameters
+
+* `room_id` - The ID of the room (e.g `!someroom:example.com`)
+
+### JSON Body Parameters
+
+* `new_room_user_id` - Required. A string representing the user ID of the user that will admin
+                       the new room that all users in the old room will be moved to.
+* `room_name` - Optional. A string representing the name of the room that new users will be
+                invited to.
+* `message` - Optional. A string containing the first message that will be sent as
+              `new_room_user_id` in the new room. Ideally this will clearly convey why the
+               original room was shut down.
+
+If not specified, the default value of `room_name` is "Content Violation
+Notification". The default value of `message` is "Sharing illegal content on
+othis server is not permitted and rooms in violation will be blocked."
+
+### Response Parameters
+
+* `kicked_users` - An integer number representing the number of users that
+                   were kicked.
+* `failed_to_kick_users` - An integer number representing the number of users
+                           that were not kicked.
+* `local_aliases` - An array of strings representing the local aliases that were migrated from
+                    the old room to the new.
+* `new_room_id` - A string representing the room ID of the new room.
+
+## Example
+
+Request:
+
+```
+POST /_synapse/admin/v1/shutdown_room/!somebadroom%3Aexample.com
+
+{
+    "new_room_user_id": "@someuser:example.com",
+    "room_name": "Content Violation Notification",
+    "message": "Bad Room has been shutdown due to content violations on this server. Please review our Terms of Service."
+}
+```
+
+Response:
+
+```
+{
+    "kicked_users": 5,
+    "failed_to_kick_users": 0,
+    "local_aliases": ["#badroom:example.com", "#evilsaloon:example.com],
+    "new_room_id": "!newroomid:example.com",
+},
+```