Allow to configure which Prometheus metrics to emit

[BarbarossaTM]

Describe the feature

Currently Bio collects a lot of metrics on different sub-systems (BGP, BMP, VRFs) and all metrics are enabled by default. It would be nice if a BGP/BMP server, could be configured to emit only desired metrics, ideally having some presets but also allowing to configure this individually.

Use cases / additional context

Usually it's better to have than to be in need, however at scale a lot of metrics can easily become an issue, for example when using Bio as a BMP receiver for a large number of routers having a lot of peer and/or full tables. In this case it would be particularly neat to be able to disable some metrics, which are less relevant (e.g. some of the BMP message type counters, etc.).