add dotnet backend

backend-dotnet/Dockerfile

@@ -0,0 +1,18 @@
+FROM mcr.microsoft.com/dotnet/sdk:8.0 AS build
+WORKDIR /src
+
+COPY *.csproj .
+RUN dotnet restore
+
+COPY . .
+RUN dotnet publish -c Release -o /app/publish
+
+FROM mcr.microsoft.com/dotnet/aspnet:8.0
+WORKDIR /app
+COPY --from=build /app/publish .
+
+EXPOSE 8000
+ENV ASPNETCORE_URLS=http://+:8000
+
+ENTRYPOINT ["dotnet", "backend-dotnet.dll"]
+