Replace string interpolation with structured logging

[lorenzophys]

Currently, the PVC autoscaler project relies on string interpolation for logging messages, making it challenging to extract meaningful data during analysis and troubleshooting. I would like to use structured fields instead of plain string interpolation.

With Logrus this is possible this way: https://github.com/sirupsen/logrus#fields

Tasks

1. Replace string interpolation with structured logging
2. Ensure that the structured fields adhere to a consistent naming convention across all log messages to facilitate easy querying and analysis.