Add HTML New Tab Page Privacy Config feature for macOS (#1152)

Task/Issue URL: https://app.asana.com/0/0/1209105499479210/f

Description:
This change adds a new case to the PrivacyFeature enum.

Sources/BrowserServicesKit/PrivacyConfig/Features/PrivacyFeature.swift

@@ -66,6 +66,7 @@ public enum PrivacyFeature: String {
     case adAttributionReporting
     case experimentTest
     case forceOldAppDelegate
+    case htmlNewTabPage
 }
 
 /// An abstraction to be implemented by any "subfeature" of a given `PrivacyConfiguration` feature.
@@ -195,3 +196,8 @@ public enum ExperimentTestSubfeatures: String, PrivacySubfeature {
     public var parent: PrivacyFeature { .experimentTest }
     case experimentTestAA
 }
+
+public enum HTMLNewTabPageSubfeature: String, Equatable, PrivacySubfeature {
+    public var parent: PrivacyFeature { .htmlNewTabPage }
+    case isLaunched
+}