Plugins: Add managed instance installation resources (#76767)

* Plugins: Add configs to allow managed install

* Expose methods to use with cloud plugin installer

* Change plugins installer bind to OSS

pkg/setting/setting_plugins.go

@@ -64,5 +64,8 @@ func (cfg *Cfg) readPluginSettings(iniFile *ini.File) error {
 	cfg.PluginsCDNURLTemplate = strings.TrimRight(pluginsSection.Key("cdn_base_url").MustString(""), "/")
 	cfg.PluginLogBackendRequests = pluginsSection.Key("log_backend_requests").MustBool(false)
 
+	// Installation token for managed plugins
+	cfg.PluginInstallToken = pluginsSection.Key("install_token").MustString("")
+
 	return nil
 }