Just (https://just.systems/) works better than make for running commands. For
example, passing arguments to `make integration-test-cli` requires a `--`
between make's arguments and the cli test runner's arguments (e.g. -sandbox),
and will also result in weird errors. Just doesn't have any of these problems.
I chose different target names than we use in the Makefile; the goal is to have
better tab completion, where the most commonly used commands can be completed
after typing a single letter. That's why I use "e2e" for integration tests,
which is not a term we use anywhere else.
Keeping the Makefile around for those who are used to it, and are too lazy to
install just.
