mpegtsmux: Add support & parameter for output KLV data to be synchronous

Aim for this change is to add synchronous KLV support to the mpegtsmux component. Have been testing this end-to-end combined with AWS Media Live / Media Package (CMAF) and have had success. A complementary change has been accepted by hls.js for extracting CMAF/KLV as output. The current async KLV is left as default, and a new parameter added to allow selection of sync or async.