Format examples as raw objects

According the the openapi spec, examples for responses and schemas should be
raw objects rather than being json strings. (It's unclear what non-json
examples should look like...).

The swagger UI used to support json strings, but no longer does. In short,
let's turn the json strings into their raw formats.

api/client-server/message_pagination.yaml

@@ -107,8 +107,7 @@ paths:
                   type: object
                   title: RoomEvent
           examples:
-            application/json: |-
-              {
+            application/json: {
                 "start": "t47429-4392820_219380_26003_2265",
                 "end": "t47409-4357353_219380_26003_2265",
                 "chunk": [