option to not initialise automatic environment activation

[Matt Broadway]

I have had a similar experience to many others (#411 #346 #265 #259) with pyenv-virtualenv being extremely slow

• adding ~200ms every time I press enter
• adding ~300ms when opening a new shell

(note I have a 16 core 9900k, my machine is not the issue. from #259 it looks like this could be related to my antivirus)

To work around this I have made a few changes to my initialisation which may be slightly hacky but they at least give me a usable shell:

export PYENV_VIRTUALENV_DISABLE_PROMPT=1
export PATH="${HOME}/.pyenv/plugins/pyenv-virtualenv/shims:${PATH}"
export PS1='(${PYENV_VERSION}) '$PS1

So I have my own version of the virtualenv prompt which seems to work well so I don't see why the default has to be so slow, but I assume it doesn't work in all cases or something?

But the main point is that I took only the PATH altering part of pyenv virtualenv-init - leaving out the prompt hook for activating local environments since I don't use them. It would be nice if I could use an official command like pyenv virtualenv-init --no-local - instead?