Configuration via environment variables or multiple files

[Delta-VII]

Hi there, first off huge thanks for your work!

Currently I'm working on a Kubernetes deployment for wg-portal. I've stumbeled on a issue with the yaml configuration file. Having sensible data like DB-passwords and LDAP Userpasswords exposed in a config file is a security risk. Because of that I'd suggest splitting the config.yaml into two files (one for critical and one for non-critical data) or adding the ability to inject secrets via a environment variable. It would also enable the usage of Docker secrets.

Let me know, what you guys think about it.