Analytics: RudderStack custom URLs to fetch SDK and Config (#41988)

* Add config options to provide custom URL to fetch Rudderstack SDK and Config

* Add new entries to defaults.ini

* Update docs

pkg/setting/setting.go

@@ -143,6 +143,8 @@ var (
 	GoogleTagManagerId      string
 	RudderstackDataPlaneUrl string
 	RudderstackWriteKey     string
+	RudderstackSdkUrl       string
+	RudderstackConfigUrl    string
 
 	// LDAP
 	LDAPEnabled           bool
@@ -945,6 +947,8 @@ func (cfg *Cfg) Load(args CommandLineArgs) error {
 	GoogleTagManagerId = analytics.Key("google_tag_manager_id").String()
 	RudderstackWriteKey = analytics.Key("rudderstack_write_key").String()
 	RudderstackDataPlaneUrl = analytics.Key("rudderstack_data_plane_url").String()
+	RudderstackSdkUrl = analytics.Key("rudderstack_sdk_url").String()
+	RudderstackConfigUrl = analytics.Key("rudderstack_config_url").String()
 	cfg.ReportingEnabled = analytics.Key("reporting_enabled").MustBool(true)
 	cfg.ReportingDistributor = analytics.Key("reporting_distributor").MustString("grafana-labs")
 	if len(cfg.ReportingDistributor) >= 100 {