[C#] aspdotnetcore (C# server) generation does not support byte/binary body

Description

When an OpenAPI spec describes the request with a body parameter of either:
schema: {
"type": "string",
"format": "binary"
}
or
schema: {
"type": "string",
"format": "byte"
}
the generated controller, correctly, has a [FromBody] System.IO.Stream or [FromBody] byte[] parameter. However, Swashbuckle out of the box does not support either type of parameter, resulting in 415 responses to any request sent, regardless of content type.

openapi-generator version

Discovered using the current git main branch.

OpenAPI declaration file content or url

'/data': {
'put': {
'parameters': [
{
"name": "data",
"in": "body",
"description": "Binary body data",
"required": true,
"schema": {
"type": "string",
"format": "byte"
}
}
}

Command line used for generation

java -jar <openapi-generator-cli.jar> generate -i <openapi.json> -g aspnetcore -o -c

Steps to reproduce

Specify an operation with the body as described above.

Related issues/PRs

Suggest a fix/enhancement

The scheme described at https://weblog.west-wind.com/posts/2017/Sep/14/Accepting-Raw-Request-Body-Content-in-ASPNET-Core-API-Controllers#Binary-Data provides a solution for forwarding the body in the appropriate format.

In addition, it is necessary to tell Swashbuckle that the content type is to be 'application/octet-stream'. (Currently OpenAPI-generator does not tell Swashbuckle the expected content type, or the response type, at all). Either a specific 'application/octect-stream' decorator (see https://stackoverflow.com/questions/41141137/how-can-i-tell-swashbuckle-that-the-body-content-is-required) or a more generic decorator in the style suggested at https://stackoverflow.com/questions/34990291/swashbuckle-swagger-how-to-annotate-content-types is needed.

Thus, there would be three steps to implement this scheme:

1. Create new .mustache files to generate the BinaryPayloadAttribute and BinaryPayloadFilter (or equivalent generic classes). The same files can be used for ASP .Net Core 2.0 and 2.1.
2. Decorate controller methods appropriately in controller.mustache.
3. In Startup.mustache, add the new filter:
   // Support binary payloads.
   c.OperationFilter();

Start with the aspnetcore generator templates, especially controller.mustache and Startup.mustache, and review how ASP.NET Core 2.0 and 2.1 templates are organized. The issue proposes adding BinaryPayloadAttribute and BinaryPayloadFilter templates, decorating generated controller methods, and registering the filter in Startup.mustache. Done means generated byte and binary body endpoints accept requests without 415 responses and advertise application/octet-stream appropriately.