Add PUID and PGID environment variables to run docker container as non-root user

[garret]

Every single LSIO docker container has this option which I think is amazing: https://docs.linuxserver.io/general/understanding-puid-and-pgid

I would like to run Focalboard as a particular user, which would solve a lot of permission issues. In all LSIO containers I just set the PUID and PGID environment variables and boom, the containers runs as that user.

Would it be possible to add such a feature? It makes managing Docker containers much easier.