Update SystemUI aconfig files to match new style

See go/sysui-aconfig-structure

Bug: 297872375
Test: build
Change-Id: Ide9ec71e572195d69f2e1995bd140b41f21e4041
diff --git a/packages/SystemUI/aconfig/systemui.aconfig b/packages/SystemUI/aconfig/systemui.aconfig
new file mode 100644
index 0000000..70832f5
--- /dev/null
+++ b/packages/SystemUI/aconfig/systemui.aconfig
@@ -0,0 +1,8 @@
+package: "com.android.systemui"
+
+flag {
+    name: "example_flag"
+    namespace: "systemui"
+    description: "An Example Flag"
+    bug: "292511372"
+}
\ No newline at end of file