Support volta installing a tarball

[rwjblue]

There are times (like when you want to test a prebuilt npm pack result) that you need to install a global package but not from the registry.

Without notion you would do npm install --global ./path/to/tarball.tgz, but notion intercepts the --global invocation errors with:

Notion error: Global package installs are not recommended

Since we are ultimately using npm install to do the heavy lifting here anyways, and npm supports:

npm install --global package-name@./some/path/to/tarball.tgz

We should be able to make something like this work (based on the work in #383):

notion install ember-cli@./ember-cli-3.10.0.tgz

However, at the moment ^ causes the following error:

error: Could not parse version "ember-cli-3.10.0.tgz"

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Reported by @Turbo87 in discord

[dherman]

@DanielRosenwasser reached out to me today with an interest in this. They have a GitHub bot that packs PRs into tarballs on demand (example), and they'd love to be able to use that in CI with Volta.

[charlespierce]

As of Volta 0.9.0, we now support using the package managers directly to install packages. We don't currently support the specific syntax volta install /path/to/tarball.tgz, but we do support npm i -g /path/to/tarball.tgz to perform the same task.

[DanielRosenwasser]

Perfect, thank you very much!