Merge "[Thread] define flag thread_user_restriction_enabled" into main

thread/flags/thread_base.aconfig

@@ -6,3 +6,10 @@ flag {
     description: "Controls whether the Android Thread feature is enabled"
     bug: "301473012"
 }
+
+flag {
+    name: "thread_user_restriction_enabled"
+    namespace: "thread_network"
+    description: "Controls whether user restriction on thread networks is enabled"
+    bug: "307679182"
+}