feat(logging): smtp debug logging

Summary

Added smtp debug logging and added config NOTIFICATION_SERVICE_SMTPLIB_LOG_LEVEL to set the log level individually

Description

When NOTIFICATION_SERVICE_ROOT_LOG_LEVEL is set to DEBUG, debug logging is automatically enabled also for smtplib (log level 2 including time stamps, c.f. https://docs.python.org/3/library/smtplib.html#smtplib.SMTP.set_debuglevel). The smtplib log level can also be controlled explicitly using the NOTIFICATION_SERVICE_SMTPLIB_LOG_LEVEL option.

Checklist

• Have the changes been tested?
  • Behavior if other services fail
• Have tests (e.g. unit tests) been adapted or new ones written?
• Has the changelog been updated?
  • Have the dependencies on other services and their versions been documented?
• Have all changes to configuration variables such as env vars been documented?
• Do all submodules point to stable branches? (develop, master/main)
• Are all pipelines completed successfully?
• Was a review completed by someone else?