Add --dry-run

[nbecker]

What's the problem this feature will solve?

Like to see what install --upgrade might do without actually proceeding with install

Describe the solution you'd like

Easiest option is add --dry-run, which would print what actions would be taken, but not actually perform any filesystem modifications.

As an example, I have a system with tensorflow-2.8. I can't update to 2.9 because I'm working with sionna, which doesn't support tf-2.9. I'm wondering if I could update tensorboard? It would be nice if I could do
pip install --upgrade tensorboard --dry-run
And see what it thinks.

Alternative Solutions

Don't know a workaround

Additional context

N/A

Code of Conduct

• I agree to follow the PSF Code of Conduct.

[pradyunsg]

Duplicate of #53.