Create a VideoFrameTrackingId RTP header extension.

Bug: webrtc:12594
Change-Id: I518b549b18143f4711728b4637a4689772474c45
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/212084
Reviewed-by: Artem Titov <titovartem@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Jeremy Leconte <jleconte@google.com>
Cr-Commit-Position: refs/heads/master@{#33567}

modules/rtp_rtcp/include/rtp_rtcp_defines.h

@@ -74,6 +74,7 @@ enum RTPExtensionType : int {
   kRtpExtensionGenericFrameDescriptor = kRtpExtensionGenericFrameDescriptor00,
   kRtpExtensionGenericFrameDescriptor02,
   kRtpExtensionColorSpace,
+  kRtpExtensionVideoFrameTrackingId,
   kRtpExtensionNumberOfExtensions  // Must be the last entity in the enum.
 };