Provide an option to export multiple pgbouncer instances with one exporter instance

[garima-trivedi]

We have a requirement to use Prometheus-community exporter but would like to run only one exporter instance instead of an exporter per PgBouncer instance.
I can see the following PR has already been opened in this direction.
#182

Please expedite the review and merge process for this PR.
Or
Please provide support for this feature.

[gabrielxfs]

+1 on this feature request