Add tailing service for Postgresql logs

When using Pebble log forwarding, logs written directly to files will not be forwarded. A pebble service should tail the postgresql logs so that they can be properly sent to Loki. The service should respect log rotation.

Start by locating the Pebble log-forwarding configuration and the PostgreSQL log files used by the operator. Trace how logs reach Loki, then define the service behavior needed for file tailing and rotation; done means rotated and newly written PostgreSQL logs are forwarded correctly.

Written by the indexing model from the issue text.