Introduce flag for palm rejection quality metrics

This flag will be used to guard framework palm rejection quality
metrics collection.

Bug: 341717757
Test: presubmit
FLAG: EXEMPT introducing flag collect_palm_rejection_quality_metrics
Change-Id: I33bdc468bc7ae57e9d1be970163517e922623c0a
diff --git a/libs/input/input_flags.aconfig b/libs/input/input_flags.aconfig
index 8e91f11..b8a8d76 100644
--- a/libs/input/input_flags.aconfig
+++ b/libs/input/input_flags.aconfig
@@ -178,3 +178,10 @@
   description: "Capture input latency metrics on a per device granular level using histograms."
   bug: "270049345"
 }
+
+flag {
+  name: "collect_palm_rejection_quality_metrics"
+  namespace: "input"
+  description: "Collect quality metrics on framework palm rejection."
+  bug: "341717757"
+}