Multiple database support - exporter does not initialize properly if one or more databases are inaccessible

[rafal-szypulka]

Thanks for adding support for multiple databases! I noticed an issue: when one or more databases are inaccessible (e.g., due to incorrect credentials or an invalid connection URL), the exporter still starts but doesn’t initialize properly. Specifically, the exporter port isn’t allocated, so you can’t query metrics even for the databases that are accessible.