volta install <package> should use latest LTS allowed by engines

[rwjblue]

Currently, running volta install some-package Volta will use some-package's engines field to decide what version of Node to pin the tool too in future invocations. Conversely, volta install node will automatically use the most recent Node LTS (not latest).

I believe that we should change the logic such that we default to using the most recent LTS that is allowed within the engines configuration for the package. Specifically, it is very common (a best practice even) that packages do not limit the upper bounds of engines because most packages work just fine across many many Node versions. This would make volta install some-package have matching behavior to volta install node.

tldr; engines usage is most commonly >= 8 or something like that, volta install choosing the latest (instead of latest LTS) means that its not uncommon (once every 6 months or so as new Node major versions are released) that folks would be installing with a Node that is fundamentally less tested/bulletproof.

[Dmitry-N-Medvedev]

I might been mistaken, but

1. LTS does not give me the latest features (e.g. class instance private methods)
2. I personally do not care if the latest node's version is not yet battle tested.