Add state param to milestone listing API (#7131)

* Support state params

* update tests

* fix tests

* add state=all support

* update tests

* update swagger

* update swagger

templates/swagger/v1_json.tmpl

@@ -3892,6 +3892,12 @@
             "name": "repo",
             "in": "path",
             "required": true
+          },
+          {
+            "type": "string",
+            "description": "Milestone state, Recognised values are open, closed and all. Defaults to \"open\"",
+            "name": "state",
+            "in": "query"
           }
         ],
         "responses": {