Place announcement-only groups behind feature flag

ts/RemoteConfig.ts

@@ -5,6 +5,7 @@ import { get, throttle } from 'lodash';
 import { connectToServerWithStoredCredentials } from './util/connectToServerWithStoredCredentials';
 
 export type ConfigKeyType =
+  | 'desktop.announcementGroup'
   | 'desktop.clientExpiration'
   | 'desktop.disableGV1'
   | 'desktop.groupCalling'

ts/models/conversations.ts

@@ -81,6 +81,7 @@ import {
 } from '../state/selectors/message';
 import { Deletes } from '../messageModifiers/Deletes';
 import { Reactions, ReactionModel } from '../messageModifiers/Reactions';
+import { isAnnouncementGroupReady } from '../util/isAnnouncementGroupReady';
 
 // TODO: remove once we move away from ArrayBuffers
 const FIXMEU8 = Uint8Array;
@@ -3016,6 +3017,10 @@ export class ConversationModel extends window.Backbone
       return false;
     }
 
+    if (!isAnnouncementGroupReady()) {
+      return false;
+    }
+
     const members = getConversationMembers(this.attributes);
     return members.every(conversationAttrs =>
       Boolean(conversationAttrs.capabilities?.announcementGroup)

ts/util/isAnnouncementGroupReady.ts

@@ -0,0 +1,11 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import * as RemoteConfig from '../RemoteConfig';
+
+export function isAnnouncementGroupReady(): boolean {
+  return Boolean(
+    RemoteConfig.isEnabled('desktop.worksAtSignal') ||
+      RemoteConfig.isEnabled('desktop.announcementGroup')
+  );
+}