Easier debugging of swagger doc rendering

Is your feature request related to a problem? Please describe.
I sometimes help debug why a swagger document doesn't render properly in the API Catalog. It is not easy, there is not good logging to show how the swagger doc is queried and transformed by the API Catalog server, and there is no information in the UI except for sometimes a very generic error that it could not be retrieved.

Describe the solution you'd like
Better logging server side, ideally without requiring debug mode (errors should be logged regardless).

I'd also like better information in the UI. Sometimes there is an error message in the UI, but it is usually not actually relevant and is always the same error message. Sometimes the substitute swagger is shown (e.g. if no swaggerUrl is present), but we should also indicate why the substitute was shown (error retrieving swagger vs no url given).

Describe alternatives you've considered

Additional context

Start by tracing how the API Catalog server retrieves and transforms Swagger documents, then inspect the UI paths for retrieval errors and substitute Swagger. Define the logging and user-facing distinctions for retrieval failures versus a missing swaggerUrl; done means both server-side diagnostics and specific UI explanations are present.