We should extend the spfx doctor command to allow users to specify the version of SPFx they want to check the compatibility for. This is useful, when you want to install a specific version of the SPFx generator, but first need to know which Node version you'll need. Right now, you can only specify SharePoint environment, but the SPFx version is detected automatically, which requires unnecessarily complex workarounds to find out the version of prerequisites you need for the specific version of SPFx.

Proposal:

Add new option --spfxVersion [spfxVersion] which accepts a version of the SPFx generator to check compatibility for. If the version doesn't match any of the supported version, the command will return an error.