How would this feature be useful?
Currently, it seems that the new 1.2.0 version of poetry has some pretty serious bugs. To avoid these, I have rolled back to the earlier 1.1.15 version. I use pipx to manage this, which works great, but now, if I use pipx upgrade-all, it will also upgrade poetry back to the newer version that I don't want to use. I use pipx for quite a few different utilities, so using pipx upgrade-all to keep everything up to date is a common part of my workflow.

Describe the solution you'd like
It seems like an additional option for pipx install could be introduced (something like --pin), that would make it so the package will not be upgraded when running pipx upgrade-all. I'm not sure how "unpinning" would be handled, and it would probably also be important to have additional feedback that a package is pinned when running pipx list, for example.

Alternatively, maybe a new pipx pin subcommand could be added that would be used to manage "pinning/unpinning" specific packages.

Describe alternatives you've considered
Obviously, it is possible to just upgrade individual packages, or rollback poetry after it gets upgraded, but it is pretty annoying to have to do that.