Rename metrics to adhere to Prometheus metric naming conventions

[stanhu]

Thanks for this project! We're looking at shipping a PgBouncer exporter in GitLab but noticed the metric names in this exporter don't adhere to Prometheus naming conventions: https://prometheus.io/docs/practices/naming/

https://github.com/spreaker/prometheus-pgbouncer-exporter#exported-metrics is an example of how the metrics should be named.

The avg queries can probably also be omitted as well, since Prometheus can calculate averages over any time period needed.

[larseen]

Yeah, agree with the points made, unfortunately the project have not seen some work in some time.
You are welcome to make a Pull Request If you like!