Feat Request: Expose more ENV vars for docker

[JigSawFr]

Hi there,
It could be nice to expose more env vars for Docker,
So we can pre-populate config fields of install directly with custom or use default if empty/not exist.

Vars to expose:

• DB_HOST (text)
• DB_PORT (text)
• DB_NAME (text)
• DB_PREFIX (text)
• DB_USER (text)
• DB_PASS (text)
• ADMIN_EMAIL (text)
• ADMIN_USER (text)
• ADMIN_PASS (text)
• PLEX_SSL (bool)
• PLEX_URL (text)
• PLEX_PORT (text)
• PLEX_TOKEN (text)

Thanks ! :)