Add Kubernetes CI/CD pipeline for kub-stage

Dockerfile

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+FROM mcr.microsoft.com/dotnet/sdk:9.0 AS build
+WORKDIR /src
+COPY src/*.sln ./ 2>/dev/null || true
+COPY src/*/*.csproj ./
+RUN for file in *.csproj; do mkdir -p "${file%.*}" && mv "$file" "${file%.*}/"; done 2>/dev/null || true
+RUN dotnet restore "FrontOffice.BFF/FrontOffice.BFF.csproj" || dotnet restore
+COPY src/ ./
+RUN dotnet publish "FrontOffice.BFF/FrontOffice.BFF.csproj" -c Release -o /app/publish
+
+FROM mcr.microsoft.com/dotnet/aspnet:9.0 AS runtime
+WORKDIR /app
+COPY --from=build /app/publish .
+ENV ASPNETCORE_URLS=http://+:8080
+EXPOSE 8080
+ENTRYPOINT ["dotnet", "FrontOffice.BFF.dll"]