Add Transfer-Encoding in OpenApi document

[jander-msft]

In the OpenAPI document, Should add Transfer-Encoding: chunked to all responses that return streamed data with indeterminate length. This may help OAS tooling to understand to return Stream types rather than fixed length deserialization.

Re: OAI/OpenAPI-Specification#1576 (comment)

[wiktork]

We should be already doing this. Sample from /trace:

Content-Disposition: attachment; filename=20210318_190121_25328.nettrace
Content-Type: application/octet-stream
Date: Thu, 18 Mar 2021 19:01:21 GMT
Server: Kestrel
Transfer-Encoding: chunked

Edit: My mistake, you mean the openapi spec, not the response itself.