ODataRoutingSample openAPI

[swurzinger]

Describe the bug
The openAPI reference implementation in ODataRoutingSample seems to have issues:

1. there seem to be two different implementations. One as middleware (ODataOpenApiMiddleware) and one as controller (ODataOpenApiController). Not sure if latter is even used?
2. The middleware implementation seems faulty/incomplete. v2 and v3 models do work, but v1 doesn't.

Reproduce steps
perform a GET request http://localhost:5000/v1/$openapi (other versions work)

Request/Response

System.NotSupportedException: Specified method is not supported.
   at ODataRoutingSample.OpenApi.ODataPathTranslater.Translate(ODataPathTemplate pathTemplate, IEdmModel model) in sample\ODataRoutingSample\OpenApi\ODataPathTranslater.cs:line 107
   at ODataRoutingSample.OpenApi.OpenApiDocumentExtensions.CreateDocument(HttpContext context, String prefixName) in sample\ODataRoutingSample\OpenApi\OpenApiDocumentExtensions.cs:line 70
   at ODataRoutingSample.OpenApi.ODataOpenApiMiddleware.ProcessOpenApiAsync(HttpContext context, String prefixName) in sample\ODataRoutingSample\OpenApi\ODataOpenApiMiddleware.cs:line 82
   at ODataRoutingSample.OpenApi.ODataOpenApiMiddleware.Invoke(HttpContext context) in sample\ODataRoutingSample\OpenApi\ODataOpenApiMiddleware.cs:line 66
   at Microsoft.AspNetCore.OData.Routing.ODataRouteDebugMiddleware.Invoke(HttpContext context) in src\Microsoft.AspNetCore.OData\Routing\ODataRouteDebugMiddleware.cs:line 80
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddlewareImpl.Invoke(HttpContext context)

Expected behavior
OpenAPI json

some explanation of the OpenAPI implementation would also be nice (e.g.: why do we use a custom IODataPathProvider and what does it do)