Use SWH_LOG_LEVELS instead of manually computing a LOG_LEVEL

SWH components supports the usage of SWH_* properties.

We should replace all the (LOGLEVEL, LOG_LEVEL) environment variables mentions and remove the (LOGLEVEL, LOG_LEVEL) computations in the image entry points.

For example:

• https://gitlab.softwareheritage.org/swh/infra/swh-apps/-/blob/master/apps/swh-lister/entrypoint.sh?ref_type=heads#L19
• https://gitlab.softwareheritage.org/swh/infra/swh-apps/-/blob/master/apps/swh-lister/Dockerfile?ref_type=heads#L31
• https://gitlab.softwareheritage.org/swh/infra/ci-cd/swh-charts/-/blob/production/swh/templates/listers/deployment.yaml?ref_type=heads#L102-103