CDN: Adds support for serving assets over a CDN (#30691)

* CDN: Initial poc support for serving assets over a CDN

* Minor fix

* added build path and test

* fix lint error

* Added edition to cdn path

* Move master builds to a separate path

* Added error handling for the url parsing, changed setting name, and added docs

* Updated sample.ini

* Some property renames

* updated

* Minor update to html

* index template improvements

* Update docs/sources/administration/configuration.md

Co-authored-by: achatterjee-grafana <70489351+achatterjee-grafana@users.noreply.github.com>

* Update docs/sources/administration/configuration.md

Co-authored-by: achatterjee-grafana <70489351+achatterjee-grafana@users.noreply.github.com>

* Added ContentDeliveryPrefix to Licence service

* updated docs

* Updated test mock

Co-authored-by: achatterjee-grafana <70489351+achatterjee-grafana@users.noreply.github.com>

conf/sample.ini

@@ -67,6 +67,9 @@
 # Unix socket path
 ;socket =
 
+# CDN Url
+;cdn_url =
+
 #################################### Database ####################################
 [database]
 # You can configure the database connection by specifying type, host, name, user and password