How would this feature be useful?
With the completion of #660 , the possibility now exists to re-create one or more pipx-managed environments based on the output of pipx list --json.

This would be useful for backup or versioning across one or more machines. For instance, I could use the output of pipx list --json from workstation A to quickly provision workstation B or laptop C with a same/very similar set of tools.

Describe the solution you'd like
I don't have firm opinions on the API here, but i would kind of naively expect pipx install-all my-pipx-list.json, which creates the new subcommand install-all, with name parity with existing -all sub-command equivalents.

Tricky points I can think of:

• what if workstation B has a different version of one or more of the top-level packages in the exported list? who wins?
• what if there are interpreter version incompatibilities in a top-level package or one or more (potentially pinned) deps or injected packages?
• what about packages installed from local tarballs, etc?

Describe alternatives you've considered
JSON is supposed to be human readable, right? :) I could certainly hack something together with zsh and jq that walks the tree and installs root + injected, but it seems natural enough to absorb this into pipx itself.