Fix OptionsRepository API test to add option by attribute_id

[bcerban]

Description

Users reported being unable to add multiple configurable product options via API. The solution is to use the attribute ID instead of attribute code in the request body. I've updated the API functional test to reflect correct usage.

Fixed Issues

1. Cannot add multiple options to configurable product via REST API #5580: Cannot add multiple options to configurable product via REST API

Manual testing scenarios

1. See Cannot add multiple options to configurable product via REST API #5580 (comment)

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-cicd2]

All committers have signed the CLA.

[okorshenko]

Good catch! We will execute extended test suite against these changes

[magento-engcom-team]

Hi @okorshenko, thank you for the review.
ENGCOM-1096 has been created to process this Pull Request