Add blog post about changes in WS command entity/source (#1904)

* Add blog post about changes in WS command entity/source

* Add example

blog/2023-09-12-ws-entity-source-simplified.md

@@ -0,0 +1,41 @@
+---
+author: Erik Montnémery
+authorURL: https://github.com/emontnemery
+title: "The websocket command entity/source has been modified"
+---
+
+The websocket command `entity/source` has been greatly simplified:
+- It's no longer possible to get information for a single entity
+- Only the domain of the entities is included in the response, `custom_component`, `config_entry` and `source` are no longer present.
+
+### New response example
+```json
+{
+  "light.entity_1": {
+    "domain": "template",
+  },
+  "switch.entity_2": {
+    "domain": "shelly",
+  },
+}
+```
+
+### Old response example
+```json
+{
+  "light.entity_1": {
+    "custom_component": false,
+    "domain": "template",
+    "source": "platform_config",
+  },
+  "switch.entity_2": {
+    "custom_component": false,
+    "config_entry": "<config_entry_id>",
+    "domain": "shelly",
+    "source": "config_entry",
+  },
+}
+```
+
+
+The change was introduced in [core PR#99439](https://github.com/home-assistant/core/pull/99439)