Service camera.onvif_ptz: add Speed option

Onvif Camera component supports Pan, Tilt and Zoom through the camera.onvif_ptz service:

However, onvif standard has also the option to control the Speed of the Pan and tilt operation (see here, under Velocity):

https://www.onvif.org/ver20/ptz/wsdl/ptz.wsdl

onvif-py3 library seems to support this:

Particularly:

def move_up(ptz, request, timeout=1):
print(‘move up…’)
request.Velocity.PanTilt._x = 0
request.Velocity.PanTilt._y = YMAX
perform_move(ptz, request, timeout

It would be nice to have an additional option in the camera.onvif_ptz service to be able to control the speed.