videotestsrc - default colorimetry of GRAY is YCbCt

consider setting the default for GRAY8 to RGB 0-255 and not 16-235
maybe add new dedicated Y800 format ? they are not the same

<Shekel> #one GRAY8 pixel
<Shekel> gst-launch-1.0 videotestsrc pattern=white is-live=1 \
<Shekel>  ! "video/x-raw, format=GRAY8, width=1, height=1, framerate=1/1" \
<Shekel>  ! identity dump=1 silent=false ! fakesink 
<Shekel> 
<Shekel> 00000000 (0x56454cbf3ed0): eb 00 00 00                                      ....            
...
<ndufresne> Shekel: ... why eb rather then ff, that looks like it's assumed that this is YCbCt 4:0:0 in limited range
<ndufresne> That seems a bit bogus since the colorimetry field isn't set
<ndufresne> Shekel: mind filling a bug report ?
<ystreet00> GstVideoInfo chooses some default colorimetry based on different factors :)
<ndufresne> remains that I believe videotestsrc should repose it
<ndufresne> as it's called GRAY8 and not Y8, the choice of using limited range is surprising
<ndufresne> s/repose/report
<ndufresne> ystreet00: or maybe there is a bug, https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/-/blob/master/gst-libs/gst/video/video-info.c#L151
<ndufresne> that should pick 0_255 range