Add `option` key to the documentation

Add `option ` key to the documentation

- Update the keys summary: https://github.com/scanapi/website/blob/main/_docs_v1/specification/api_specification_keys.md
- Create a file called `option.md` [here](https://github.com/scanapi/website/tree/main/_docs_v1/specification) to explain how to use `options` key.

Options Key: https://github.com/scanapi/scanapi/pull/552