Add support for sharing cached installs across jobs

[kyle-leonhard]

Great tool! I'm also using https://github.com/Swatinem/rust-cache/tree/v2/ which supports a 'shared-key' parameter: "A cache key that is used instead of the automatic job-based key, and is stable over multiple jobs."

I'd love to use something like that with cargo-install!

Perhaps something like this: e0928/cargo-install/pull/29