Proposal: Use version requirement for slight add and slight new instead of precise version

[Mossaka]

Describe the solution you'd like

We want to give users more flexibility to download WIT interfaces and slight templates using version requirements instead of precise verion numbers.

A precise version number is defined as a three digit version number like v0.3.1 but a version requirement is much more flexible than that. A major motivation for this proposal is that we want to ignore patch versions for downloading interfaces or slight templates. That is, we want to be able to run something like

slight add [email protected]

or

slight add http-client@latest

Where v0.3 is a version requirement saying that the major version is 0 and minor version is 3 and it ignores the patch version. It will automatically find the latest version that satisifes this version requirement.

The latest version is equivalent to * wildcard version requirement which basically says "please download the latest version for me, and I don't care about major, minor, patch or whatever"

CC @danbugs

Additional context