Allow defining multiple schemas under the schemas configuration variable

[brianespinosa]

Ajv does support combining multiple schemas for validation. There are some features within json-schema like $ref which might not work properly if we are defining only a single schema. It might be good to update the schema property to be schemas and allow glob patterns like we do in files.

I am happy to look into doing this too. The attribute does make sense to rename plural like files but that would be a breaking change. LMK what your thoughts are on that.