Clarify string formats in Typing Notifications section of the CS API

Signed-off-by: Kévin Commaille <zecakeh@tedomum.fr>

data/api/client-server/typing.yaml

@@ -36,6 +36,8 @@ paths:
           example: "@alice:example.com"
           schema:
             type: string
+            format: mx-user-id
+            pattern: "^@"
         - in: path
           name: roomId
           description: The room in which the user is typing.
@@ -43,6 +45,8 @@ paths:
           example: "!wefh3sfukhs:example.com"
           schema:
             type: string
+            format: mx-room-id
+            pattern: "^!"
       requestBody:
         content:
           application/json:

data/event-schemas/schema/m.typing.yaml

@@ -13,6 +13,8 @@ properties:
         type: array
         items:
           type: string
+          format: mx-user-id
+          pattern: "^@"
         description: The list of user IDs typing in this room, if any.
     required:
     - user_ids