res/res_pjsip_outbound_registration: Add registration statistics for StatsD

This patch adds outbound registration statistics for StatsD. This includes
the following:
 * A GUAGE metric for the overall count of outbound registrations.
 * A GUAGE metric for each state an outbound registration can be in. As the
   outbound registrations change state, the overall count of how many
   outbound registrations are in the particular state is changed.

These statistics are particularly useful for systems with a large number of
SIP trunks, and where measuring the change in state of the trunks is useful
for monitoring.

ASTERISK-25571

Change-Id: Iba6ff248f5d1c1e01acbb63e9f0da1901692eb37

1 files changed, 13 insertions, 4 deletions

diff --git a/CHANGES b/CHANGES
index 4a55a06ff..348927b1d 100644
--- a/CHANGES
+++ b/CHANGES
@@ -36,10 +36,19 @@ Dialplan Functions
 
 res_pjsip_outbound_registration
 -------------------------------
-* A new 'fatal_retry_interval' option has been added to outbound registration.
-  When set (default is zero), and upon receiving a failure response to an
-  outbound registration, registration is retried at the given interval up to
-  'max_retries'.
+ * A new 'fatal_retry_interval' option has been added to outbound registration.
+   When set (default is zero), and upon receiving a failure response to an
+   outbound registration, registration is retried at the given interval up to
+   'max_retries'.
+
+ * If res_statsd is loaded and a StatsD server is configured, basic statistics
+   regarding the state of outbound registrations will now be emitted. This
+   includes:
+   - A GUAGE statistic for the overall number of outbound registrations, i.e.:
+       PJSIP.registrations.count
+   - A GUAGE statistic for the overall number of outbound registrations in a
+     particular state, e.g.:
+       PJSIP.registrations.state.Registered
 
 res_pjsip
 ------------------