chore: update docker image

This PR introduces multiple changes:

updates node to 20
updates ruby to 2.7 (this should unblock the release pipeline)
updates dart 3.3
adds a new script that fetches a dart version that matches the platform architecture to enable building this image on m1 (arm) macs.
updates the base image to debian bullseye
introduces a new PR workflow, that builds the image, runs the generate.sh & test.sh scripts and then provides the resulting image as a downloadable tarball for local use if the Dockerfile changed.

Checklist

[ ] I have read the contributing guidelines and signed the CLA.
[ ] I have referenced an issue containing the design document if my change introduces a new feature.
[ ] I have read the security policy.
[ ] I confirm that this pull request does not address a security vulnerability. If this pull request addresses a security vulnerability, I confirm that I got approval (please contact security@ory.sh) from the maintainers to push the changes.
[ ] I have added tests that prove my fix is effective or that my feature works.
[ ] I have added the necessary documentation within the code base (if appropriate).