Add feature flag for introductions

bramble-api/src/main/java/org/briarproject/bramble/api/FeatureFlags.java

@@ -11,6 +11,8 @@ public interface FeatureFlags {
 
 	boolean shouldEnableDisappearingMessages();
 
+	boolean shouldEnableIntroductionsInCore();
+
 	boolean shouldEnablePrivateGroupsInCore();
 
 	boolean shouldEnableForumsInCore();

bramble-core/src/test/java/org/briarproject/bramble/test/TestFeatureFlagModule.java

@@ -25,6 +25,11 @@ public class TestFeatureFlagModule {
 				return true;
 			}
 
+			@Override
+			public boolean shouldEnableIntroductionsInCore() {
+				return true;
+			}
+
 			@Override
 			public boolean shouldEnablePrivateGroupsInCore() {
 				return true;

briar-android/src/main/java/org/briarproject/briar/android/AppModule.java

@@ -340,6 +340,11 @@ public class AppModule {
 				return true;
 			}
 
+			@Override
+			public boolean shouldEnableIntroductionsInCore() {
+				return true;
+			}
+
 			@Override
 			public boolean shouldEnablePrivateGroupsInCore() {
 				return true;

briar-core/src/main/java/org/briarproject/briar/introduction/IntroductionModule.java

@@ -1,5 +1,6 @@
 package org.briarproject.briar.introduction;
 
+import org.briarproject.bramble.api.FeatureFlags;
 import org.briarproject.bramble.api.cleanup.CleanupManager;
 import org.briarproject.bramble.api.client.ClientHelper;
 import org.briarproject.bramble.api.contact.ContactManager;
@@ -35,12 +36,14 @@ public class IntroductionModule {
 	@Singleton
 	IntroductionValidator provideValidator(ValidationManager validationManager,
 			MessageEncoder messageEncoder, MetadataEncoder metadataEncoder,
-			ClientHelper clientHelper, Clock clock) {
+			ClientHelper clientHelper, Clock clock, FeatureFlags featureFlags) {
 		IntroductionValidator introductionValidator =
 				new IntroductionValidator(messageEncoder, clientHelper,
 						metadataEncoder, clock);
-		validationManager.registerMessageValidator(CLIENT_ID, MAJOR_VERSION,
+		if (featureFlags.shouldEnableIntroductionsInCore()) {
-				introductionValidator);
+			validationManager.registerMessageValidator(CLIENT_ID, MAJOR_VERSION,
+					introductionValidator);
+		}
 		return introductionValidator;
 	}
 
@@ -52,7 +55,11 @@ public class IntroductionModule {
 			ConversationManager conversationManager,
 			ClientVersioningManager clientVersioningManager,
 			IntroductionManagerImpl introductionManager,
-			CleanupManager cleanupManager) {
+			CleanupManager cleanupManager,
+			FeatureFlags featureFlags) {
+		if (!featureFlags.shouldEnableIntroductionsInCore()) {
+			return introductionManager;
+		}
 		lifecycleManager.registerOpenDatabaseHook(introductionManager);
 		contactManager.registerContactHook(introductionManager);
 		validationManager.registerIncomingMessageHook(CLIENT_ID,

briar-headless/src/main/java/org/briarproject/briar/headless/HeadlessModule.kt

@@ -107,6 +107,7 @@ internal class HeadlessModule(private val appDir: File) {
         override fun shouldEnableImageAttachments() = false
         override fun shouldEnableProfilePictures() = false
         override fun shouldEnableDisappearingMessages() = false
+        override fun shouldEnableIntroductionsInCore() = false
         override fun shouldEnablePrivateGroupsInCore() = false
         override fun shouldEnableForumsInCore() = true
         override fun shouldEnableBlogsInCore() = true