doent core write files

1. https://www.c-sharpcorner.com/article/sending-files-from-web-api/

2. https://blog.johnwu.cc/article/ironman-day23-asp-net-core-upload-download-files.html

3.https://stackoverflow.com/questions/39994695/asp-net-core-api-controller-response-body-writeasync-base64-string-not-working