Add force old app delegate flag (#1141)

Task/Issue URL:
https://app.asana.com/0/414235014887631/1208832732122403/f
iOS PR: [n/a](duckduckgo/iOS#3727)
macOS PR: n/a 
What kind of version bump will this require?: Major

**Description**:
Simple privacy config flag that will allow us to use old app delegate in
case of any issues.

Sources/BrowserServicesKit/PrivacyConfig/Features/PrivacyFeature.swift

@@ -65,6 +65,7 @@ public enum PrivacyFeature: String {
     case textZoom
     case adAttributionReporting
     case experimentTest
+    case forceOldAppDelegate
 }
 
 /// An abstraction to be implemented by any "subfeature" of a given `PrivacyConfiguration` feature.