OpenAPI document missing some externalDocs descriptions

[lcawl]

#4772 added support for improved link text for external documentation links in the OpenAPI output.

However, it looks like in some cases the information is not propagated to the output. For example, in
#5409 the link text should be "Time units" but it's the default "External documentation". This might be because the externalDocs in this case is in a schema object, whereas the working scenarios are in operations.