Set the "Accept" request header to the specified type, rathern than a…

[Numpsy]

…lways ApplicationJson

When doing some tests with a client for an API that returns plain text, I noticed that the Accept header on SwaggerProvider requests always seemed to be set to application/json rather than the text type specified in the OpenApi spec, and then I saw this checking if retMime is specified but then always using ApplicationJson and wondered if that's correct?

If this is an issue then maybe it could also be tested with something like

[<Route("api/[controller]")>]
[<ApiController>]
type ReturnCsvController() =
    inherit ControllerBase()

    [<HttpGet; Produces("text/csv")>]
    member this.Get() =
        if this.Request.Headers.Accept.Equals("text/csv") then
            "Hello,world" |> ActionResult<string>
        else
            ActionResult<string>(UnsupportedMediaTypeResult())

?

[sergey-tihon]

I am OK with the fix, can you please add controller here https://github.com/fsprojects/SwaggerProvider/blob/master/tests/Swashbuckle.WebApi.Server/Controllers/ReturnTextControllers.fs and tests that verify it:

[Numpsy]

Added a couple of extra tests with controller functions that check the Accept header (two tests rather than one just to test that it handles switching rather than always being one or the other)

[sergey-tihon]

Does it fix #291 ?

[Numpsy]

This one is just about the Accept header, I think the Content-Type on stream content would be something like ad8d2a8 (I didn't have time to test it much beyond that)