Switch from CircleCI to GitHub Actions

[Shinigami92]

Investigate the test structure
Try to move away from CircleCI if applicable
Try to use native GitHub Actions instead

[Shinigami92]

GitHub actions are managed in the repo through config files. Most of the checks seem to be running on CircleCI though.

I'll see what we can do with higher privileges.

@goce-cz I know, when I have access to GitHub Actions configuration (I mean branch protections and CI rules) then I will try to manage and rewrite the CI using https://docs.github.com/en/actions/using-containerized-services/creating-postgresql-service-containers

[Shinigami92]

I will leave this issue open to remind me to change the readme badges and fully delete circle ci stuff like the webhook

[Shinigami92]

Webhook removed