feat: Add validation command

[gmpinder]

Adds JSON Schema validation for the recipes. This will print out a list of errors encountered when the recipe does not match the schema.

In order to get the schema to validate properly, we had to include the requirement of having source set to local on a locally built module. The validate command will be put under a feature flag until the v0.9 release to prevent breaking user's configs.

[xynydev]

Should we implement recipe v2 next, and the announce all the breaking changes at once?
Like:

• You should now refactor your recipes (which will automatically opt in to recipe validation)
• But if you don't want to do that, you don't need to (yet?)
  • But if you want to opt in to recipe validation for recipe v1, you still need to add source: local for local modules

If we want a version: key for example, would it be possible to make the presence of version: 1 opt in to recipe validation for v1 recipes? Then to use v2 one would need to specify version: 2, also enabling validation.

[gmpinder]

If we want a version: key for example, would it be possible to make the presence of version: 1 opt in to recipe validation for v1 recipes? Then to use v2 one would need to specify version: 2, also enabling validation.

I think this is a great idea to opt-in! The user shouldn't need to know the schema url to take advantage of validation (though it would be needed if they want the validation in their editors).

[gmpinder]

Should we implement recipe v2 next, and the announce all the breaking changes at once?

Yeah I think that would be a good step. I think getting validate and new/init commands should be the last things before the v0.9 release. I'd also like to fix the whole distrobox issue #160 too, but could use some help with that since I don't use distrobox much.