This patch adds a few CLI commands to the res_prometheus module to aid
system administrators setting up and configuring the module. This includes:
* prometheus show status: Display basic statistics about the Prometheus
module, including its essential configuration, when it was last scraped,
and how long the scrape took. The last two bits of information are useful
when Prometheus isn't generating metrics appropriately, as it will at
least tell you if Asterisk has had its HTTP route hit by the remote
server.
* prometheus show metrics: Dump the current metrics to the CLI. Useful for
system administrators to see what metrics are currently available without
having to cURL or go to Prometheus itself.
ASTERISK-28403
Change-Id: Ic09813e5e14b901571c5c96ebeae2a02566c5172
