Add new bucket to bluetooth pairing result metrics.

Bug: b/175707921
Change-Id: I9f54d970e45ffb6a8cee83f3b70aa5f6f75f8bbf

Corresponding BlueZ metrics implementation can be found at: https://chromium-review.googlesource.com/c/chromiumos/third_party/bluez/+/2595924

Change-Id: I9f54d970e45ffb6a8cee83f3b70aa5f6f75f8bbf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2595525Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Yu Liu <yudiliu@google.com>
Cr-Commit-Position: refs/heads/master@{#837883}

tools/metrics/histograms/enums.xml

@@ -7210,6 +7210,7 @@ Called by update_bad_message_reasons.py.-->
   <int value="10" label="Authentication cancelled"/>
   <int value="11" label="Authentication timeout"/>
   <int value="12" label="Unknown"/>
+  <int value="13" label="BT IO connection failed"/>
 </enum>
 
 <enum name="BlueZResultOfPerProfileConnection">