themes/luan: Show Python virtualenv

[Askaiant]

Edited the prompt so it shows the active python virtualenv to the user when it is active.

[akinomyoga]

Thanks for the contribution. I have been thinking that what would be shown in the prompt would largely depend on personal preferences, so I have been marking the PRs that try to add an element to the prompt as customization examples. However, particularly for the virtualenv and the condaenv, we have so many similar PRs including this one, #387, #373, #335, and #282.

Now maybe we should introduce a configuration variable like OMB_PROMPT_SHOW_PYTHON_VENV=true, etc., and include the venv elements in all the themes. One non-trivial stuff is that we need to carefully choose the design of the new element that matches each theme one by one. Hmm, maybe we can give up supporting it all at once and separately apply PRs to the themes that the PR has appeared.

[Askaiant]

I see what you mean. I will close this PR in place of #394. This way we could give the option to personalize whether the prompt is shown or not. As for including the element in the theme, this could be done progressively per request (e.g. #372 , #117 , #210 , #387 , #373 and #335 ) but would have to somehow match the style, would be happy to help.