Add dry-run feature flag to test incremental rollouts on iOS #502

Task/Issue URL: https://app.asana.com/0/0/1205431733474504/f
iOS PR: duckduckgo/iOS#2008
macOS PR: duckduckgo/macos-browser#1623
What kind of version bump will this require?: Patch

Description:
Adds dry-run feature flag to test incremental rollouts on iOS, based off of process used to test macOS

Sources/BrowserServicesKit/PrivacyConfig/Features/PrivacyFeature.swift

@@ -41,6 +41,7 @@ public enum PrivacyFeature: String {
     case incontextSignup
     case newTabContinueSetUp
     case networkProtection
+    case incrementalRolloutTest2 // Temporary feature flag for testing incremental rollouts
 }
 
 /// An abstraction to be implemented by any "subfeature" of a given `PrivacyConfiguration` feature.
@@ -72,3 +73,11 @@ public enum NetworkProtectionSubfeature: String, Equatable, PrivacySubfeature {
     case waitlist
     case waitlistBetaActive
 }
+
+public enum IncrementalRolloutTestSubfeature2: String, PrivacySubfeature {
+     public var parent: PrivacyFeature {
+         .incrementalRolloutTest2
+     }
+
+     case rollout
+ }