CCM-11580: add limit parameter to list letters endpoint

Author: m-houston

specification/api/components/parameters/limit.yml

@@ -0,0 +1,9 @@
+name: page
+in: query
+description: |-
+  The ordinal number of the page of results to be retrieved. If omitted, the
+  first page of results will be returned. Use the links section in the response
+  body to determine whether any further pages of results exist.
+schema:
+  type: number
+  example: 1