Factor out all the common parameters of the various /relations apis

This doesn't currently work, perhaps because the template needs to
resolve refs?

Also, the other instances of the params need to be replaced with the
refs and the response fields probably should be factored out too.

data/api/client-server/relations.yaml

@@ -33,69 +33,12 @@ paths:
       security:
         - accessToken: []
       parameters:
-        - in: path
-          name: roomId
-          description: The ID of the room containing the parent event.
-          required: true
-          example: "!636q39766251:matrix.org"
-          schema:
-            type: string
-        - in: path
-          name: eventId
-          description: The ID of the parent event whose child events are to be returned.
-          required: true
-          example: $asfDuShaf7Gafaw
-          schema:
-            type: string
-        - in: query
-          name: from
-          description: |-
-            The pagination token to start returning results from. If not supplied, results
-            start at the most recent topological event known to the server.
-
-            Can be a `next_batch` or `prev_batch` token from a previous call, or a returned
-            `start` token from [`/messages`](/client-server-api/#get_matrixclientv3roomsroomidmessages),
-            or a `next_batch` token from [`/sync`](/client-server-api/#get_matrixclientv3sync).
-          required: false
-          example: page2_token
-          schema:
-            type: string
-        - in: query
-          name: to
-          description: |-
-            The pagination token to stop returning results at. If not supplied, results
-            continue up to `limit` or until there are no more events.
-
-            Like `from`, this can be a previous token from a prior call to this endpoint
-            or from `/messages` or `/sync`.
-          required: false
-          example: page3_token
-          schema:
-            type: string
-        - in: query
-          name: limit
-          description: |-
-            The maximum number of results to return in a single `chunk`. The server can
-            and should apply a maximum value to this parameter to avoid large responses.
-
-            Similarly, the server should apply a default value when not supplied.
-          required: false
-          example: 20
-          schema:
-            type: integer
-        - in: query
-          name: dir
-          x-addedInMatrixVersion: "1.4"
-          description: |-
-            Optional (default `b`) direction to return events from. If this is set to `f`, events
-            will be returned in chronological order starting at `from`. If it
-            is set to `b`, events will be returned in *reverse* chronological
-            order, again starting at `from`.
-          schema:
-            type: string
-            enum:
-              - b
-              - f
+        - $ref: '#/components/parameters/roomId'
+        - $ref: '#/components/parameters/eventId'
+        - $ref: '#/components/parameters/from'
+        - $ref: '#/components/parameters/to'
+        - $ref: '#/components/parameters/limit'
+        - $ref: '#/components/parameters/dir'
       responses:
         # note: this endpoint deliberately does not support rate limiting, therefore a
         # 429 error response is not included.
@@ -508,3 +451,73 @@ servers:
 components:
   securitySchemes:
     $ref: definitions/security.yaml
+  parameters:
+    roomId:
+        in: path
+        name: roomId
+        description: The ID of the room containing the parent event.
+        required: true
+        example: "!636q39766251:matrix.org"
+        schema:
+          type: string
+    eventId:
+        in: path
+        name: eventId
+        description: The ID of the parent event whose child events are to be returned.
+        required: true
+        example: $asfDuShaf7Gafaw
+        schema:
+          type: string
+    from:
+        in: query
+        name: from
+        description: |-
+          The pagination token to start returning results from. If not supplied, results
+          start at the most recent topological event known to the server.
+
+          Can be a `next_batch` or `prev_batch` token from a previous call, or a returned
+          `start` token from [`/messages`](/client-server-api/#get_matrixclientv3roomsroomidmessages),
+          or a `next_batch` token from [`/sync`](/client-server-api/#get_matrixclientv3sync).
+        required: false
+        example: page2_token
+        schema:
+          type: string
+    to:
+        in: query
+        name: to
+        description: |-
+          The pagination token to stop returning results at. If not supplied, results
+          continue up to `limit` or until there are no more events.
+
+          Like `from`, this can be a previous token from a prior call to this endpoint
+          or from `/messages` or `/sync`.
+        required: false
+        example: page3_token
+        schema:
+          type: string
+    limit:
+        in: query
+        name: limit
+        description: |-
+          The maximum number of results to return in a single `chunk`. The server can
+          and should apply a maximum value to this parameter to avoid large responses.
+
+          Similarly, the server should apply a default value when not supplied.
+        required: false
+        example: 20
+        schema:
+          type: integer
+    dir:
+        in: query
+        name: dir
+        x-addedInMatrixVersion: "1.4"
+        description: |-
+          Optional (default `b`) direction to return events from. If this is set to `f`, events
+          will be returned in chronological order starting at `from`. If it
+          is set to `b`, events will be returned in *reverse* chronological
+          order, again starting at `from`.
+        schema:
+          type: string
+          enum:
+            - b
+            - f