Describe the bug

API analyzers should flag an undeclared 200 status code, and provide an option to fix it.

To Reproduce

Steps to reproduce the behavior:

1. Using ASP.NET Core 3.0 with analyzers enabled

<PropertyGroup>
 <IncludeOpenAPIAnalyzers>true</IncludeOpenAPIAnalyzers>
</PropertyGroup>

2. Run this code (adapted from this sample with the ProducesResponseType attribute removed)

// GET api/contacts/{guid}
[HttpGet("{id}", Name = "GetById")]
public IActionResult Get(string id)
{
    var contact = _contacts.Get(id);

    if (contact == null)
    {
        return NotFound();
    }

    return Ok(contact);
}

3. The API analyzer flags the NotFound using a warning (this is expected).
4. The API analyzer does not flag the return Ok(...); (not expected)

Expected behavior

4. The API analyzer does flag the return Ok(...) using a warning.
5. An option to fix this warning is provided, choosing it adds the following attribute
   [ProducesResponseType(typeof(Contact), StatusCodes.Status200OK)]

Why I think this is a bug

From the docs:

The analyzers package notifies you of any controller action that:

• Returns an undeclared status code.
• Returns an undeclared success result.

Additional context

Follow up to dotnet/AspNetCore.Docs#15269 (comment)

.NET Core SDK: 3.0.100
.NET Core runtimes installed:
Microsoft.NETCore.App 3.0.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 3.0.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]