channel-folders: Create two channel folders in the dev database.

Adds a visible example to the PATCH /channel_folders endpoint for
reordering an organization's channel folders. So that the example
works in a normal dev environment, we also add a second channel
folder when populating the dev database.

(cherry picked from commit 4f4923ef2b)

zerver/openapi/zulip.yaml

@@ -25132,6 +25132,7 @@ paths:
                     folders.
                   items:
                     type: integer
+                  example: [2, 1]
               required:
                 - order
             encoding: