Add Django structlog settings

Description

Instead of repeating the same "DevOps" structlog settings, incorporate into library and provide means to enable (or auto-enable).

Acceptance criteria

• LOG_LEVEL ENV sets logging level (support strings and ints)
• Document that LOG_LEVEL must be set as a true env var
• Generate log warning for using EXTERNAL_SETTINGS_LOB_LEVEL
• DRY means to set structlog settings in django (minimal settings.py entry required)
• Example Django app added to this project to excercise these additions
• get_structlog_logger works consistently with Django and non-Django projects