Enhancement of Documentation within API OAS yaml

[PedroDiez]

Problem description

Improve API Documentation to be included in "description" of API OAS (yaml)

Possible evolution

Based on current input in:

• https://github.com/camaraproject/CarrierBillingCheckOut/blob/main/documentation/API_documentation/Carrier_Billing_API.md
• https://github.com/camaraproject/CarrierBillingCheckOut/blob/main/documentation/API_documentation/resources/Carrier_Billing_State_Engine.JPG

Adapt and move that info into "description" param of API OAS yaml.

Additional context

This action is to follow commonalities recommendation to have APIs with fully autocontained description

[PedroDiez]

25/OCT: To be included in next PR generation

[PedroDiez]

Closed as per PR#119 MERGED