Percolate the verbose global option to the silent argument for session installation commands, and document it

[agriyakhetarpal]

This PR documents the existing nox.options.verbose option and makes verbose a flag pair. Based on its value, it flips the silent parameter for session.install(<...>) and conda_install(<...>) to expose outputs to stdout/stderr.

The standard rule for flag pairs applies (as I understand it): the silent parameter if set takes precedence over the value of nox.options.verbose, and the --verbose/--no-verbose CLI arguments will take precedence over both the values of nox.options.verbose and of silent whether set or not.

Please let me know if this is not desirable; in that case, I can close this PR.

Thank you for your time!

Closes #741

Note

My original ask with the linked issue was to do both things: add a nox.options.verbose option to be able to specify that in a Noxfile, and also to not need to set session.install(silent=False) for every command; i.e., also print the output of installation commands (i.e., in order to adhere to the "all output of all commands run is shown, regardless of the silent argument" sentence in the docs by including these installation commands as a part of all commands).

It appears that since then, the verbose option has been added; however, the installation commands were not taking this option's value into account, and this PR only addresses this part.

[agriyakhetarpal]

Thanks for triggering the CI! I've fixed the docs build.

[agriyakhetarpal]

I'm not sure what triggered the KeyboardInterrupt for the macos-13 job, it would be helpful if it could be re-triggered. Thanks!