Docs: clarify the description of actions_allow_post_url (#95995)

* Docs: clarify the description of actions_allow_post_url

* adding a word to clarify this extends the default behavior and doesn't replace it

* Update docs/sources/setup-grafana/configure-grafana/_index.md

Co-authored-by: Beverly Buchanan <131809838+BeverlyJaneJ@users.noreply.github.com>

* Update docs/sources/setup-grafana/configure-grafana/_index.md

Co-authored-by: Beverly Buchanan <131809838+BeverlyJaneJ@users.noreply.github.com>

---------

Co-authored-by: Beverly Buchanan <131809838+BeverlyJaneJ@users.noreply.github.com>

docs/sources/setup-grafana/configure-grafana/_index.md

@@ -689,7 +689,9 @@ Set the policy template that will be used when adding the `Content-Security-Poli
 
 ### actions_allow_post_url
 
-Sets API paths to be accessible between plugins using the POST verb. This is a comma separated list, and uses glob matching.
+Sets API paths to be accessible between plugins using the POST verb. If the value is empty, you can only pass remote requests through the proxy. If the value is set, you can also send authenticated POST requests to the local server. You typically use this to enable backend communication between plugins.
+
+This is a comma-separated list which uses glob matching.
 
 This will allow access to all plugins that have a backend: