Prepend to PATH instead of overwriting it

[sinopeus]

We set PATH in the template project (not the templated project)'s devcontainer.json so that the container venv's bin directory is added to the path, but do it by overwriting the PATH variable instead of the better practice, prepending to it. This is because we weren't able to get it to work when prepending it. See discussion.

Ideally we would be able to prepend to PATH.

[lsorber]

Should be solved with v1.2.0!