Extract developer site (#5249)

* Extract developer site

* Fix title in sidebar

* Update dev section reference

* Update edit in github link on help page

source/developers/api.markdown

@@ -9,13 +9,6 @@ sharing: true
 footer: true
 ---
 
-Home Assistant provides various APIs. For detail please refer to [Home Assistant API](https://dev-docs.home-assistant.io/en/dev/) documentation.
-
-  * [Python API](https://dev-docs.home-assistant.io/)
-  * [WebSocket API](/developers/websocket_api/)
-  * [REST API](/developers/rest_api/)
-  * [Python REST API](/developers/python_api/)
-  * [Server-sent events](/developers/server_sent_events/)
-
-If you are not using the [`frontend`](/components/frontend/) in your setup then you need to enable the components by adding them to your `configuration.yaml` file. E.g., [`websocket_api:`](/components/websocket_api/) for the WebSocket API or [`api:`](/components/api/) for the [REST API](/developers/rest_api/) and the [Python REST API](/developers/python_api/).
-
+<script>
+window.location = 'https://developers.home-assistant.io/docs/en/external_api_rest.html';
+</script>