net core 发布docker镜像的官方写法

使用vscode发布的镜像可能存在不能运行的问题， 可以去docker的官方文档下找一个标准的格式再替换一下就可以用了：

FROM mcr.microsoft.com/dotnet/core/sdk:2.2 AS build-env
workdir /app

# copy csproj and restore as distinct layers
copY *.csproj ./
RUN dotnet restore

# copy everything else and build
copY . ./
RUN dotnet publish -c Release -o out

# Build runtime image
FROM mcr.microsoft.com/dotnet/core/aspnet:2.2
workdir /app
copY --from=build-env /app/out .
ENTRYPOINT ["dotnet", "aspnetapp.dll"]