web.FileResponse support charset

[cole-dda]

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

When send file to browser, browser require charset ，such as：

'text/plain;charset=utf-8' is better than 'text/plain'

'text/html;charset=utf-8' is better than 'text/html'

💡 Describe the solution you'd like

web_fileresponse.py

line 323

  charset="utf-8"  #pass by parameter
  self.content_type = ct +";"+charset  # type: ignore

📋 Additional context

[webknjaz]

feel free to send a PR