feat: Dockerize, allow anonymous usage, use postgresql

[libnewton]

• This allows optional usage of Parachute without any login (activate via the respective env var)
• Switch to postgres for better performance and for a more modern database.
• Add quick Docker setup
• Remove hardcoded parachute.fyi in favour of dynamic hostname determination
• Optionalize most env vars (todo: make the UI reflect this!)

@maintainer feel free to modify this PR as you like. I would be quite happy if there would be a zero-login way to use Parachute, like it's the case with the original when2meet.
I am very sure that this can be implemented much better than this hacked-together version.

[louisunlimited]

@libnewton Hey there! Thank you for contributing! We're happy to see this project gaining attractions from devs like you! While we greatly appreciate this pr, we are still working very hard to make our first stable release of the site and also figuring out community contrib. guidelines and stuff. We do plan to put some of your suggested features on our road map since we are currently doing some big changes to the underlying infra -> like switching to clerk for auth.

Whilst we can't guarantee anything at this time, feel free to open these features as issues and we can then talk about them in detail or even put them on our future roadmap! We hope to release our first public stable version this month and finishing up our community guidelines so we can welcome more passionate developers like you to contribute!