imagefreeze: Copy GstCapsFeatures to caps for source pad
imagefreeze: Copy GstCapsFeatures to caps for source pad

Allows using imagefreeze with buffers in GLMemory. The following pipeline
works.

gst-launch-1.0 filesrc location=image.jpg ! jpegdec ! glupload ! \
imagefreeze ! glcolorconvert ! glimagesinkelement

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/-/merge_requests/594>

GStreamer/gst-plugins-good,GStreamer/gst-plugins-good,GStreamer/gst-plugins-good,GStreamer/gst-plugins-good