Add a way to use --window-position

[watchydev]

I'm using a RPI 4 with its dual display outputs and would like to run the program twice to display a separate dashboard on each monitor.

[vgb1993]

same here

[RyuunosukeDS3]

This would be REALLY game changing for me.
I've tried to implement it myself but i've NEVER coded in golang before...
So, apparently it DID recognize the option, but it didn't move the window:

grafana-kiosk --URL http://myip:3000/ --login-method local --username myuser --password mypass --kiosk-mode full --window-position 300x300
2021/06/25 08:38:21 No config specified, using environment and args
2021/06/25 08:38:21 AutoFit: true
2021/06/25 08:38:21 LXDEEnabled: false
2021/06/25 08:38:21 LXDEHome: /home/pi
2021/06/25 08:38:21 Mode: full
2021/06/25 08:38:21 URL: http://172.30.0.5:3000/
2021/06/25 08:38:21 LoginMethod: local
2021/06/25 08:38:21 Username: myuser
2021/06/25 08:38:21 Password: *redacted*
2021/06/25 08:38:21 IgnoreCertificateErrors: false
2021/06/25 08:38:21 WindowPosition 300x300
2021/06/25 08:38:21 IsPlayList: false
2021/06/25 08:38:21 AutoFit: true
2021/06/25 08:38:21 LXDEEnabled: false
2021/06/25 08:38:21 LXDEHome: /home/pi
2021/06/25 08:38:21 Mode: full
2021/06/25 08:38:21 URL: http:/myip:3000/
2021/06/25 08:38:21 LoginMethod: local
2021/06/25 08:38:21 Username: myuser
2021/06/25 08:38:21 Password: *redacted*
2021/06/25 08:38:21 IgnoreCertificateErrors: false
2021/06/25 08:38:21 WindowPosition 300x300
2021/06/25 08:38:21 IsPlayList: false
2021/06/25 08:38:21 DISPLAY= :0
2021/06/25 08:38:21 XAUTHORITY= /run/user/1000/gdm/Xauthority
2021/06/25 08:38:21 method  local
2021/06/25 08:38:21 Launching local login kiosk
2021/06/25 08:38:21 KioskMode: Fullscreen
2021/06/25 08:38:21 Navigating to  http://myip:3000/?kiosk=1&autofitpanels