ci: add lint for checks metadata

[nikpivkin]

This PR adds an invalid_metadata rule to help maintain consistency, avoid errors, and enforce metadata standards. This will help to avoid such mistakes: #327 (comment)

[simar7]

nice, should we also add a linter for naming of checks? Ref #327 (comment)

Maybe we allow only certain kinds of checks, based on providers: AVD-AWS-*, AVD-DS-*, etc. So that if there's one that we don't know, we'd have to add it to the lint rule first, if it is a legitimate addition of a new provider.