Add displayName to urls and use that in drop-down list

Thanks to #3649, now the API name is used to generate a direct link to that API, also fixing the deep linking problem when multiple APIs are present. The API name becomes a parameter in the URL, as it is visible in the drop-down list when the Swagger UI renders multiple API definitions.

I'm proposing to add a new optional property in the list of the API definitions, next to name or primaryName, called displayName (eventually also primaryDisplayName) to be solely used as visible text in the drop-down.

Having friendly API names like "Customer look-up v1" generates URLs with escaped characters. Changing the API name would also break links. The APIs should be named "customer-lookup-v1" to fix and make the URL more robust, but then the drop-down doesn't look as human-friendly as before.

My proposal is to introduce a new parameter to fix the (cosmetic) display issue.

Start by locating the API definition list and drop-down rendering, then trace how name and primaryName are currently used for visible text and URL generation. The change is done when an optional displayName can control the drop-down label while the API name remains stable for links, with the existing behavior preserved when it is absent.