Built-in Prometheus stats exporter and Grafana template [ISC-support #14725]

Please add a feature to export Kea statistics to Prometheus Please publish a Grafana template for displaying the statistics in a useful way. (I will open a separate ticket for this, but the two should be tested together).

Some initial questions

• Are you sure your feature is not already implemented in the latest Kea version? Yes

• Are you sure what you would like to do is not possible using some other mechanisms? It is possible to manually import the Kea stats into Prometheus but this would make it easier, more automatic. It is also possible to implement a Prometheus client in Kea. This is more work, a tighter integration and is not what I am asking for here.

• Have you discussed your idea on kea-users or kea-dev mailing lists? No. But if we are about to implement it, I would be happy to ask on Kea-users if people want it. This was requested by an ISC Kea support customer.

Is your feature request related to a problem? Please describe. It would be nice if we could simplify the process of exporting and displaying Kea statistics for users of these two popular open source projects (Prometheus and Grafana).

Describe the solution you'd like User can enable stats export to Prometheus. User must install Prometheus and configure Prometheus 'target' system information in Kea User may optionally select/tailor which statistics to export, or use the reasonable default we establish.

Describe alternatives you've considered An alternative would be implementing a Prometheus client.https://prometheus.io/docs/instrumenting/clientlibs/

Additional context https://prometheus.io/docs/instrumenting/exporters/

Direct link: support#14725