Investigate universal use of direnv for devcontainers

[thclark]

Feature request

In the windquest-infrastructure devcontainer @nvn-nil added:

RUN apt-get update && apt-get install -y \
    direnv \
    && rm -rf /var/lib/apt/lists/*

RUN echo 'eval "$(direnv hook bash)"' >> ~/.bashrc
RUN echo 'eval "$(direnv hook bash)"' >> ~/.bash_profile

Perhaps if this is beneficial we should make it a stock feature? It would have to be wired to zsh in order to work with our default devcontainer terminal.