Early return if no product.attribute.value is to be imported

When updating product.product records, product_tmpl_id is set to False in values if not specified in the import type.
But we don't want to set it to False as the value already exists in the odoo_record

Not forcing required default value if required_keys_ignore_mapper and required_keys are defined in options.mapper.
Adding the new property required_keys_ignore_mapper in order to override the result of required_keys function