OpenAPI compliance: avoid $ref siblings (#1457)

This strives to fix all remaining cases where additional attributes
(most often 'description' but not only) are provided next to $ref
by wrapping $ref in allOf; and also drops allOf in a couple of places
where $ref is the only element under it.

data/api/client-server/definitions/errors/rate_limited.yaml

@@ -11,23 +11,24 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-$ref: error.yaml
-type: object
-title: RateLimitError
-description: The rate limit was reached for this request
-properties:
-  errcode:
-    type: string
-    description: The M_LIMIT_EXCEEDED error code
-    example: M_LIMIT_EXCEEDED
-  error:
-    type: string
-    description: A human-readable error message.
-    example: Too many requests
-  retry_after_ms:
-    type: integer
-    description: |-
-      The amount of time in milliseconds the client should wait
-      before trying the request again.
-    example: 2000
-required: ["errcode"]
+allOf:
+  - $ref: error.yaml
+  - type: object
+    title: RateLimitError
+    description: The rate limit was reached for this request
+    properties:
+      errcode:
+        type: string
+        description: The M_LIMIT_EXCEEDED error code
+        example: M_LIMIT_EXCEEDED
+      error:
+        type: string
+        description: A human-readable error message.
+        example: Too many requests
+      retry_after_ms:
+        type: integer
+        description: |-
+          The amount of time in milliseconds the client should wait
+          before trying the request again.
+        example: 2000
+    required: ["errcode"]

data/api/client-server/definitions/event_batch.yaml

@@ -16,9 +16,7 @@ properties:
   events:
     description: List of events.
     items:
-      allOf:
-      - $ref: ../../../event-schemas/schema/core-event-schema/event.yaml
-      type: object
+      $ref: ../../../event-schemas/schema/core-event-schema/event.yaml
     type: array
 type: object
 title: EventBatch

data/api/client-server/definitions/push_rule.yaml

@@ -38,8 +38,7 @@ properties:
   conditions:
     type: array
     items:
-      allOf:
-      - $ref: push_condition.yaml
+      $ref: push_condition.yaml
     description: |-
       The conditions that must hold true for an event in order for a rule to be
       applied to an event. A rule with no conditions always matches. Only