Add .NET Core 2.1 versions

worker/dotnet/Dockerfile

@@ -0,0 +1,16 @@
+FROM microsoft/dotnet:2.1-sdk as builder
+
+WORKDIR /Worker
+COPY Worker/Worker.csproj .
+RUN dotnet restore
+
+COPY /Worker .
+RUN dotnet publish -c Release -o /out Worker.csproj
+
+# app image
+FROM microsoft/dotnet:2.1-runtime
+
+WORKDIR /app
+ENTRYPOINT ["dotnet", "Worker.dll"]
+
+COPY --from=builder /out .