docs: update QOS docs to include QOS messages
docs: update QOS docs to include QOS messages

Add some docs about the values needed for a QoS message and some use
cases.

See #322947

magcius/gstreamer,Distrotech/gstreamer,krieger-od/gstreamer,krieger-od/gstreamer,mparis/gstreamer,ensonic/gstreamer,Lachann/gstreamer,cablelabs/gstreamer,collects/gstreamer,collects/gstreamer,magcius/gstreamer,krichter722/gstreamer,ahmedammar/platform_external_gst_gstreamer,cfoch/gstreamer,ylatuya/gstreamer,drothlis/gstreamer,ahmedammar/platform_external_gst_gstreamer,lubosz/gstreamer,lovebug356/gstreamer,shelsonjava/gstreamer,lovebug356/gstreamer,mparis/gstreamer,magcius/gstreamer,krieger-od/gstreamer,lubosz/gstreamer,lubosz/gstreamer,ylatuya/gstreamer,cablelabs/gstreamer,drothlis/gstreamer,Distrotech/gstreamer,lubosz/gstreamer,surround-io/gstreamer,ylatuya/gstreamer,mrchapp/gstreamer,krichter722/gstreamer,krieger-od/gstreamer,ahmedammar/platform_external_gst_gstreamer,mparis/gstreamer,shelsonjava/gstreamer,lovebug356/gstreamer,Lachann/gstreamer,StreamUtils/gstreamer,jpakkane/gstreamer,jpxiong/gstreamer,Lachann/gstreamer,shelsonjava/gstreamer,jpakkane/gstreamer,ensonic/gstreamer,centricular/gstreamer,cfoch/gstreamer,krichter722/gstreamer,Distrotech/gstreamer,jpakkane/gstreamer,drothlis/gstreamer,shelsonjava/gstreamer,cablelabs/gstreamer,cfoch/gstreamer,justinjoy/gstreamer,jpxiong/gstreamer,jpakkane/gstreamer,StreamUtils/gstreamer,mrchapp/gstreamer,cablelabs/gstreamer,collects/gstreamer,mparis/gstreamer,mparis/gstreamer,collects/gstreamer,ensonic/gstreamer,drothlis/gstreamer,jpxiong/gstreamer,StreamUtils/gstreamer,magcius/gstreamer,surround-io/gstreamer,krieger-od/gstreamer,Lachann/gstreamer,mrchapp/gstreamer,drothlis/gstreamer,StreamUtils/gstreamer,ylatuya/gstreamer,surround-io/gstreamer,justinjoy/gstreamer,jpakkane/gstreamer,centricular/gstreamer,justinjoy/gstreamer,cfoch/gstreamer,surround-io/gstreamer,centricular/gstreamer,surround-io/gstreamer,collects/gstreamer,jpxiong/gstreamer,cablelabs/gstreamer,StreamUtils/gstreamer,krichter722/gstreamer,Distrotech/gstreamer,jpxiong/gstreamer,krichter722/gstreamer,ensonic/gstreamer,justinjoy/gstreamer,centricular/gstreamer,Lachann/gstreamer,lubosz/gstreamer,justinjoy/gstreamer,centricular/gstreamer,Distrotech/gstreamer,ylatuya/gstreamer,lovebug356/gstreamer,ensonic/gstreamer,mrchapp/gstreamer,shelsonjava/gstreamer,cfoch/gstreamer,mrchapp/gstreamer,ahmedammar/platform_external_gst_gstreamer,magcius/gstreamer,lovebug356/gstreamer,ahmedammar/platform_external_gst_gstreamer