Add instructions for uploading OAS to Konnect Dev Portal

[djjazzyjew]

Where is the problem?

https://docs.konghq.com/konnect/api-products/service-documentation/#api-specification

What happened?

There aren't instructions to guide users to upload an OAS file to their API Product Version. Instead it is buried in a page titled "Dev Portal Service Documentation". This also needs to be updated to reflect the new naming of "API Products".

What did you expect to happen?

The docs should reflect the current process of uploading an OAS file in the following page in API Products:

The page title should also be changed to "Dev Portal API Product Documentation"

Code of Conduct and Community Expectations

• I agree to follow this project's Code of Conduct
• I agree to abide by the Community Expectations

[lena-larionova]

Fixed in #6616.