[API] Issue Search Add filter for MilestoneNames (#16173)

templates/swagger/v1_json.tmpl

@@ -1876,6 +1876,12 @@
             "name": "labels",
             "in": "query"
           },
+          {
+            "type": "string",
+            "description": "comma separated list of milestone names. Fetch only issues that have any of this milestones. Non existent are discarded",
+            "name": "milestones",
+            "in": "query"
+          },
           {
             "type": "string",
             "description": "search string",