Cap the number of incrementalMacs populated in an envelope.

Add a remote config `global.maxIncrementalMacsPerEnvelope` (client
fallback of 10) that limits how many attachment pointers in a single
envelope can have their incrementalMac field populated. Each
incrementalMac can be up to 8 KiB, so having too many risks exceeding
the 96 KiB envelope size threshold. Excess attachment pointers have
their incrementalMac and chunkSize fields stripped.

app/src/main/java/org/thoughtcrime/securesms/dependencies/ApplicationDependencyProvider.java

@@ -176,6 +176,7 @@ public class ApplicationDependencyProvider implements AppDependencies.Provider {
                                             Optional.of(new SecurityEventListener(context)),
                                             SignalExecutors.newCachedBoundedExecutor("signal-messages", ThreadUtil.PRIORITY_IMPORTANT_BACKGROUND_THREAD, 1, 16, 30),
                                             RemoteConfig.maxEnvelopeSizeBytes(),
+                                            RemoteConfig.maxIncrementalMacsPerEnvelope(),
                                             RemoteConfig::useMessageSendRestFallback,
                                             RemoteConfig.useBinaryId(),
                                             BuildConfig.USE_STRING_ID);

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

@@ -1182,6 +1182,15 @@ object RemoteConfig {
     hotSwappable = true
   )
 
+  /** The maximum number of attachment pointers that can have incrementalMac populated in a single envelope. */
+  @JvmStatic
+  @get:JvmName("maxIncrementalMacsPerEnvelope")
+  val maxIncrementalMacsPerEnvelope: Int by remoteInt(
+    key = "global.maxIncrementalMacsPerEnvelope",
+    defaultValue = 10,
+    hotSwappable = true
+  )
+
   /** Whether or not to send over binary service ids (alongside string service ids). */
   @JvmStatic
   @get:JvmName("useBinaryId")