Fix for External Storage Uploads from gxObject SD Rest Services

[ggallotti]

• Enable Buffering for .NET in order to External Storage Clients (S3, Azure) to be able to handle the Stream for uploading.
• Add UnitTests for gxObject Upload Service to S3.
• Add Methods for setting External Storage programatically. (for UnitTesting)

Amazon.S3.AmazonS3Exception: Could not determine content length
   at Amazon.S3.Model.Internal.MarshallTransformations.PutObjectRequestMarshaller.GetStreamWithLength(Stream baseStream, Int64 hintLength)
   at Amazon.S3.Model.Internal.MarshallTransformations.PutObjectRequestMarshaller.Marshall(PutObjectRequest putObjectRequest)
   at Amazon.S3.Model.Internal.MarshallTransformations.PutObjectRequestMarshaller.Marshall(AmazonWebServiceRequest input)
   at Amazon.Runtime.Internal.Marshaller.PreInvoke(IExecutionContext executionContext)
   at Amazon.Runtime.Internal.Marshaller.InvokeAsync[T](IExecutionContext executionContext)
   at Amazon.S3.Internal.AmazonS3PreMarshallHandler.InvokeAsync[T](IExecutionContext executionContext)
   at Amazon.Runtime.Internal.CallbackHandler.<>n__0[T](IExecutionContext executionContext)
   at Amazon.Runtime.Internal.CallbackHandler.InvokeAsync[T](IExecutionContext executionContext)
   at Amazon.S3.Internal.AmazonS3ExceptionHandler.InvokeAsync[T](IExecutionContext executionContext)
   at Amazon.Runtime.Internal.ErrorCallbackHandler.InvokeAsync[T](IExecutionContext executionContext)
   at Amazon.Runtime.Internal.MetricsHandler.InvokeAsync[T](IExecutionContext executionContext)
   at GeneXus.Storage.GXAmazonS3.ExternalProviderS3.PutObject(PutObjectRequest request)
   at GeneXus.Storage.GXAmazonS3.ExternalProviderS3.UploadSimple(String fileName, Stream stream, GxFileType destFileType)
   at GeneXus.Storage.GXAmazonS3.ExternalProviderS3.Upload(String fileName, Stream stream, GxFileType destFileType)
   at GxExternalFileInfo.Create(Stream data)
   at GxFile.Create(Stream data)

Azure Exception:

System.NotSupportedException: Specified method is not supported.
   at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.HttpRequestStream.set_Position(Int64 value)
   at GeneXus.Storage.GXAzureStorage.AzureStorageExternalProvider.Upload(String fileName, Stream stream, GxFileType fileType)
   at GxExternalFileInfo.Create(Stream data)
   at GxFile.Create(Stream data)

[genexusbot]

Cherry pick to beta success

• 2c5c37b

[genexusbot]

Cherry pick to beta failed, 2 conflicted files in commit 83cfdab

• dotnet/test/DotNetCoreUnitTest/DotNetCoreUnitTest.csproj
• dotnet/test/DotNetCoreUnitTest/Middleware/RestServiceTest.cs

[genexusbot]

Cherry pick to beta failed, 1 conflicted file in commit 83cfdab

• dotnet/test/DotNetCoreUnitTest/DotNetCoreUnitTest.csproj