2023-01-17: Support `lts/-X` Version Notation

Is your feature request related to a problem? Please describe.

I want to be able to specify versions in CI configs which are relative to the current LTS version, so that I can test against multiple LTS versions without needing to change the CI config when new versions are released.

Describe the solution you'd like

I want to be able to use lts/-X version notation. This notation is supported by nvm, and allows for specifying offsets from the current LTS version, e.g. currently LTS is v18, so lts/-1 is v16.

Supporting the same notation as nvm would be helpful for consistency with cross-platform CI jobs.

Describe alternatives you've considered

I have not considered any alternatives.