[AppCast][1/N] Add Feature Flag for App Casting

Add a feature flag for the App Casting APIs which will be introduced into TaskCo ntinuityManager

Flag: android.companion.enable_remote_app_access
Bug: 400970610
Test: Manual Testing
Change-Id: I1c31395ed4c38e5d7c964f0a70d1a11aff36ef90
diff --git a/core/java/android/companion/flags.aconfig b/core/java/android/companion/flags.aconfig
index 7398e48..2156ca8 100644
--- a/core/java/android/companion/flags.aconfig
+++ b/core/java/android/companion/flags.aconfig
@@ -103,3 +103,11 @@
     description: "Enable medical profile"
     bug: "414859687"
 }
+
+flag {
+    name: "enable_remote_app_access"
+    is_exported: false
+    namespace: "desktop_better_together"
+    description: "Enable the Remote App Access API"
+    bug: "400970610"
+}