Add ability to list tags

[avylove]

How would this feature be useful?

When providing a Nox configuration for a team that may not be familiar with Nox, it would be good to give a simple command to list tags rather than have them look in the nox configuration or document them seperately.

Describe the solution you'd like

A new cli option, list-tags, which will list sessions by tag

$ nox --list-tags

lint:
  * flake8 -> Run flake8
  * pylint -> Run pylint
format:
  * black -> Run black
  * isort -> Run isort
check:
  * black -> Run black
  * flake8 -> Run flake8
  * isort -> Run isort 
  * pylint -> Run pylint
  * test -> Run tests

Describe alternatives you've considered

Tags could be added to the current list output, but, for larger projects, it may be unclear which sessions fall under which tags. Perhaps this could be solved by coloring the tags, but I think a tag view for list would be more useful.

Instead of a separate command line option, it could be added to the bottom of the existing output.

Anything else?

No response

[henryiii]

You can programmatically get the tags with #665 :)