FEAT: make loglevel configurable

[ColmTalbot]

This PR makes the log level configurable in the pipeline. This is basically following the method described in https://www.structlog.org/en/stable/bound-loggers.html#filtering-by-log-levels.

[JBorrow]

Looks good but make the default log level DEBUG for this stage of the project. Also, how are these configurable in practice? export SOTRPLIB_LOG_LEVEL=DEBUG?

[JBorrow]

Just checking in to see if you managed to test whether this correctly reads from environment variables?

[ColmTalbot]

Just checking in to see if you managed to test whether this correctly reads from environment variables?

I verified that SOTRP_LOG_LEVEL={DEBUG,INFO,WARNING} (case insensitive, but note SOTRP not SOTRPLIB) works.

[JBorrow]

That's correct. Thank you!