Add prometheus metrics endpoint

[tewing]

Is your feature request related to a problem? Please describe.
Polaris should expose a prometheus metrics endpoint. This would allow prometheus to know the health of polaris and alert if it is unhealthy.

Describe the solution you'd like
http://${POLARIS_POD_IP}/metrics

[sudermanjr]

Potential metrics:

• Checks run
• Dashboard refreshes

[akosveres]

In addition I'd like to add the power of alerting to this issue, having the polaris dashboard is nice, but we're not going to watch the dashboard every single day, it would be good to have the option of setting up automatic alerts based off the metrics and alert teams owning the services.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.