Update filesize markdown for config flow (#21960)

source/_integrations/filesize.markdown

@@ -9,6 +9,8 @@ ha_release: 0.64
 ha_domain: filesize
 ha_platforms:
   - sensor
+ha_codeowners:
+  - '@gjohansson-ST'
 ---
 
 The `filesize` sensor is for displaying the size in MB of a file.
@@ -19,20 +21,4 @@ File paths must also be added to [allowlist_external_dirs](/docs/configuration/b
 
 </div>
 
-## Configuration
-
-To enable the `filesize` sensor, add the following lines to your `configuration.yaml`:
-
-```yaml
-sensor:
-  - platform: filesize
-    file_paths:
-      - /config/home-assistant_v2.db
-  ```
-
-{% configuration %}
-file_paths:
-  description: The absolute path to the file.
-  required: true
-  type: list
-{% endconfiguration %}
+{% include integrations/config_flow.md %}