[MM-57966]Centralize the 200 maximum page size cap for the per_page parameter and remove individual mentions from API endpoint documentation (#26859)

api/v4/source/channels.yaml

@@ -1307,7 +1307,7 @@
             default: 0
         - name: per_page
           in: query
-          description: The number of members per page. There is a maximum limit of 200 members.
+          description: The number of members per page.
           schema:
             type: integer
             default: 60