Support "previews" for zero byte responses in API explorer

[nateKlaux]

Feature Description

Support "zero byte" or "no response" responses in the API explorer's response preview. Currently, file preview says "File preview not supported for application/octet-stream".

Use Case

Some endpoints return no response and we've had some feedback that the "File preview not supported..." message created confusion/FUD that there was an error. Just showing a blank response with the 2xx status code should alleviate this.

For reference, we define this behavior in OAS with no content: property:

      responses: 
        '200':  
          description: Request processed successfully, but no content in the response.

Proposed Experience (Optional)

Display a blank/empty text box. For instance, swagger just shows: