Multi-distro support for common script, refactor, fixes

[Chuxel]

This PR refactors the common script to support Debian/Ubuntu, RedHat/Fedora, and Alpine based images.

Rather than having one massive script, it also refactors it into multiple parts for better maintainability.

Since in the Alpine case, we cannot assume bash is present, it bootstraps using sh in install.sh and then, after installing bash, execs main.sh where the core logic exists.

In addition, due to the performance impact of the "dirty" flag in the prompt, this is now moved behind an option and off by default.

Finally, the theme was renamed "devcontainers" rather than codespaces, though a symlink is in place for back compat.