Publishing unlisted API reference

[julia-rabello]

Is your feature request related to a problem? Please describe.
Publishing unlisted API reference is still a challenge in the current version of Developer Portal, resulting in leaving API reference from an internal repository fully unpublished and using a workaround that is not entirely appropriate for unlisted API scenarios. More details below.

Describe the solution you'd like
It would be nice to be able to publish unlisted documentation of non-public APIs from our internal repository (openapi-schemas-internal), including their overview page, as we did in the previous version of Developer Portal. This is particularly useful for alpha and closed beta products that need API reference to support testers without listing it publicly on the portal or in our public openapi-schemas repository.

Describe alternatives you've considered
The current workaround is to document APIs that should be internal on openapi-schemas and not list them on Dev Portal navigation. However, this is not ideal, because it is a public repository and the API overview page still shows up as a result on on Google Search (e.g. Profile System API which is in closed beta, see image below).