Detect and generate correct content-type headers for input files

[timayabi2020]

Currently for cmdlets that upload files, the media content-type headerhas been set to null for all file types. Therefore the API treats such requests as an application/octet-stream.

There needs to be a feature that will automatically detect the file type and append the correct content-type header to the request.

Related issue is here on autorest Azure/autorest.powershell#1286

[timayabi2020]

Closing this as it was fixed in #2570