Add ability to set execution user on Docker Image

[salomj]

Is your feature request related to a problem? Please describe.
Permissions issues when performing actions

Describe the solution you'd like
Ability to set user either using --user $(id -u kapowarr):$(id -g kapowarr) or --env PUID=$(id -u kapowarr) --env PGID=$(id -g kapowarr)

Additional context
Kapowarr crashes when you try to force set the user using --user $(id -u kapowarr):$(id -g kapowarr)