[Feature Request] Allow setting default theme via docker compose.

[spthiel]

Is your feature request related to a problem? Please describe.
I am developing a docker setup for a small team and would like to theme yacht to the default of our project instead of having it default to green

Describe the solution you'd like
Some way to set the values of the default theme (i.e. by writing a json to the docker environment variables or storing a file.json somewhere with the theme as content.

Describe alternatives you've considered
Alternative would be for each user to set the theme themself but I'd rather if this wasn't required

Additional context
-