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/api/frontendsettings_test.go

@@ -166,7 +166,7 @@ func TestHTTPServer_GetFrontendSettings_pluginsCDNBaseURL(t *testing.T) {
 		{
 			desc: "With CDN",
 			mutateCfg: func(cfg *setting.Cfg) {
-				cfg.PluginsCDNURLTemplate = "https://cdn.example.com/{id}/{version}/public/plugins/{id}/{assetPath}"
+				cfg.PluginsCDNURLTemplate = "https://cdn.example.com"
 			},
 			expected: settings{PluginsCDNBaseURL: "https://cdn.example.com"},
 		},