wifi.proto: Add metrics for failed SAR sensor reg

This commit adds the metric for counting failures in registration of
SAR sensor listener.

Bug: 65174506
Test: Unit tests

Change-Id: I8d13336aa9c433128f500063819081cfcc43d2cc
Signed-off-by: Ahmed ElArabawy <arabawy@google.com>
diff --git a/proto/src/wifi.proto b/proto/src/wifi.proto
index 33fc5e5..15c0468 100644
--- a/proto/src/wifi.proto
+++ b/proto/src/wifi.proto
@@ -470,6 +470,9 @@
   // Counts the occurrences of each link speed (Mbps) level
   // with rssi (dBm) and rssi^2 sums (dBm^2)
   repeated LinkSpeedCount link_speed_counts = 121;
+
+  // Number of times the SarManager failed to register SAR sensor listener
+  optional int32 num_sar_sensor_registration_failures = 122;
 }
 
 // Information that gets logged for every WiFi connection.
@@ -1611,4 +1614,4 @@
 
   // Firmware alert code. Only valid when the event was triggered by a firmware alert, otherwise -1.
   optional int32 firmware_alert_code = 10 [default = -1];
-}
\ No newline at end of file
+}