Start annotating which version of the spec added a thing (#3425)

* Introduce a new "added-in" template and use it on endpoints

* Use "added-in" on schema properties too

* Annotate sections of the spec with their added versions

* Demo of "added-in" on a room version (to be fleshed out)

* Use clearer versioning semantics

* Update and fix validator for Swagger custom properties

* Fix docs

data/api/server-server/definitions/event-schemas/m.device_list_update.yaml

@@ -13,6 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+x-addedInMatrixVersion: "1.1"
 type: object
 title: m.device_list_update
 description: |-

data/api/server-server/definitions/event-schemas/m.signing_key_update.yaml

@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+x-addedInMatrixVersion: "1.1"
 type: object
 title: m.signing_key_update
 description: |-

data/api/server-server/knocks.yaml

@@ -29,6 +29,7 @@ securityDefinitions:
 paths:
   "/make_knock/{roomId}/{userId}":
     get:
+      x-addedInMatrixVersion: "1.1"
       summary: Get information required to make a knock event for a room.
       description: |-
         Asks the receiving server to return information that the sending
@@ -190,6 +191,7 @@ paths:
 
   "/send_knock/{roomId}/{eventId}":
     put:
+      x-addedInMatrixVersion: "1.1"
       summary: Submit a signed knock event to a resident server.
       description: |-
         Submits a signed knock event to the resident server for it to

data/api/server-server/user_keys.yaml

@@ -178,6 +178,7 @@ paths:
                             description:
                               The display name which the user set on the device.
               master_keys:
+                x-addedInMatrixVersion: "1.1"
                 type: object
                 description: |-
                   Information on the master cross-signing keys of the queried users.
@@ -199,6 +200,7 @@ paths:
                   }
                 }
               self_signing_keys:
+                x-addedInMatrixVersion: "1.1"
                 type: object
                 description: |-
                   Information on the self-signing keys of the queried users. A map