feat: detect.Schema() should allow json arrays

[osterbit]

support should be expanded beyond csv data now that we support jsonschema

current detect.schema() allows only csv:

func Schema(r *dataset.Structure, data io.Reader) (schema *jsonschema.RootSchema, err error) {
	if r.Format == dataset.UnknownDataFormat {
		return nil, errors.New("dataset format must be specified to determine schema")
	}

	switch r.Format {
	case dataset.CSVDataFormat:
		return CSVSchema(r, data)
	default:
		return nil, fmt.Errorf("'%s' is not supported for field detection", r.Format.String())
	}
}