fix: pass environment variables down through supervisord

[DASPRiD]

#61 allowed setting GUNICORN_BIND_ADDR, but environment variables were never passed down through sudo into supervisord, so this had no effect.

This PR fixes that by passing all environment variables down to supervisord. This additionally allows to completely skip a config file and configure pretalx entirely through env variables instead.

For the time being until this is merged and released I have published a hotfixed version myself:
https://hub.docker.com/repository/docker/dasprid/pretalx-standalone/general

[almereyda]

Just noting that due to multiple issues with this repository this week I was working on an extensive production-ready rewrite of the environment to remove the Supervisor altogether.

I am in process of commiting the changes and documenting their rationale, in so we can have a community-wide conversation about where to take this repository together.

main...allmende:pretalx-docker:main

Please look out for a related Pull Request within the day.

[almereyda]

Please find

• Feat: rework Container image, Compose manifest and CI #64

for review and feedback.

[rixx]

@DASPRiD thank you for taking the time to look into this! Let's figure out how #64 is going to work out, and in case it's not getting merged, we can revisit this PR, I'd say?

[DASPRiD]

Sounds good to me.