Add iteration web URL to API response

doc/api/group_iterations.md

@@ -49,7 +49,8 @@ Example response:
     "created_at": "2020-01-27T05:07:12.573Z",
     "updated_at": "2020-01-27T05:07:12.573Z",
     "due_date": "2020-02-01",
-    "start_date": "2020-02-14"
+    "start_date": "2020-02-14",
+    "web_url": "http://gitlab.example.com/groups/my-group/-/iterations/13"
   }
 ]
 ```

doc/api/iterations.md

@@ -51,7 +51,8 @@ Example response:
     "created_at": "2020-01-27T05:07:12.573Z",
     "updated_at": "2020-01-27T05:07:12.573Z",
     "due_date": "2020-02-01",
-    "start_date": "2020-02-14"
+    "start_date": "2020-02-14",
+    "web_url": "http://gitlab.example.com/groups/my-group/-/iterations/13"
   }
 ]
 ```

ee/changelogs/unreleased/iteration-lists-frontend.yml

+---
+title: Add web_url to iterations API
+merge_request: 52178
+author:
+type: added

ee/lib/api/entities/iteration.rb

@@ -10,6 +10,10 @@ module API
       expose :state_enum, as: :state
       expose :created_at, :updated_at
       expose :start_date, :due_date
+
+      expose :web_url do |iteration, _options|
+        Gitlab::UrlBuilder.build(iteration)
+      end
     end
   end
 end

ee/spec/fixtures/api/schemas/list.json

@@ -54,7 +54,8 @@
             "id",
             "title",
             "description",
-            "state"
+            "state",
+            "web_url"
           ],
           "properties": {
             "id": {
@@ -71,6 +72,9 @@
             },
             "state": {
               "type": "integer"
+            },
+            "web_url": {
+              "type": "string"
             }
           }
         }