Add initial link+sync support.

app/src/main/java/org/thoughtcrime/securesms/util/RemoteConfig.kt

@@ -1135,5 +1135,13 @@ object RemoteConfig {
     hotSwappable = false
   )
 
+  /** Whether or not this device supports syncing data to newly-linked device. */
+  @JvmStatic
+  val linkAndSync: Boolean by remoteBoolean(
+    key = "android.linkAndSync",
+    defaultValue = false,
+    hotSwappable = true
+  )
+
   // endregion
 }