Plugins: Fix plugins CDN not working when plugins are not in domain's root path (#63202)

* Plugins CDN: Add support for different CDN root path

* Plugins CDN: Make frontendsettings return the correct CDN base path

* Update comments

* Fix version detection

* Undo frontend changes

* Fix system.js asset path construction

* fix(plugins): translate all plugin css asset paths loaded via cdn

* refactor(plugins): rename extractPluginNameVersionFromUrl and add comments

* Fix typo in comment

Co-authored-by: Will Browne <wbrowne@users.noreply.github.com>

* Hardcode CDN URL structure

/{id}/{version}/public/plugins/{id}/{assetPath} is not required anymore in the cdn url template config

---------

Co-authored-by: Jack Westbrook <jack.westbrook@gmail.com>
Co-authored-by: Will Browne <wbrowne@users.noreply.github.com>

pkg/plugins/manager/loader/loader_test.go

@@ -412,7 +412,7 @@ func TestLoader_Load(t *testing.T) {
 			name:  "Load CDN plugin",
 			class: plugins.External,
 			cfg: &config.Cfg{
-				PluginsCDNURLTemplate: "https://cdn.example.com/{id}/{version}/public/plugins/{id}/{assetPath}",
+				PluginsCDNURLTemplate: "https://cdn.example.com",
 				PluginSettings: setting.PluginSettings{
 					"grafana-worldmap-panel": {"cdn": "true"},
 				},