stasis: Add statistics gathering in developer mode.

This change adds statistics gathering to Stasis topics,
subscriptions, and message types. These can be viewed using
CLI commands and provide insight into how Stasis is used
and how long certain operations take to execute.

These are only available when Asterisk is compiled in
developer mode and do not have any impact under normal
operation.

ASTERISK-28117

Change-Id: I94411b53767f89ee01714daaecf0c2f1666e863f