[REQ] [csharp-netcore] Allow to specify content-type when sending a file

Created by: llRandom

Is your feature request related to a problem? Please describe.

Currently it's not possible to specity content-type when sending a file using csharp-netcore client. It's always sent as application/octet-stream. Other clients support it (for example, typescript-angular)

Describe the solution you'd like

A ContentType property may be added to an existing FileParameter class with application/octet-stream as a default value