glfilter: add parent meta to output buffer for input buffer
requested to merge JaredHu/gstreamer:glupload-keep-one-reference-of-input-buffer-in-dmabuf-uploader into main
glfilter will unref input buffer after _transform() call immidiately, but gpu may still reading input buffer for rendering because gl api is executed async. Need hold reference for input buffer by adding parent meta to output buffer.
Edited by Haihua Hu