clocksync: Add a new property "sync-to-first" for automatic ts-offset setup

Add a new property so that clocksync can setup "ts-offset" value
based on the first buffer and pipeline's running time when the
first arrived. Newly update "ts-offset" in this case would be
a value that allows outputting the first buffer without clock waiting.
35 jobs for !702 with clocksync-sync-first in 23 minutes and 43 seconds (queued for 7 seconds)
latest detached
Status Job ID Name Coverage
  Build Docker
passed #5777725
alpine amd64 manifest builder docker

00:00:30

passed #5777723
android docker

00:00:28

passed #5777722
cerbero fedora amd64 docker

00:00:13

passed #5777720
fedora amd64 docker

00:00:29

passed #5777727
gst-indent amd64 docker

00:00:28

 
  Preparation
passed #5777730
gst indent

00:00:09

passed #5777728
manual
manifest

00:00:19

 
  Build
passed #5777741
gstreamer
build cerbero cross-android universal

00:07:40

passed #5777745
gst-ios-13.2
build cerbero cross-ios universal

00:20:30

passed #5777742
gstreamer
build cerbero cross win32

00:06:42

passed #5777743
gstreamer
build cerbero cross win64

00:06:44

passed #5777740
gstreamer
build cerbero fedora x86_64

00:06:45

passed #5777744
gst-macos-10.15
build cerbero macos x86_64

00:09:03

passed #5777746
1809 gstreamer-windows windows docker
build cerbero msvc x86_64

00:11:21

passed #5777736
build clang fedora x86_64

00:05:54

manual #5777739
1809 windows docker allowed to fail manual
build msys2
passed #5777732
build nodebug fedora x86_64

00:03:09

passed #5777734
build static fedora x86_64

00:05:55

passed #5777735
build static nodebug fedora x86_64

00:03:09

passed #5777737
1809 windows docker
build vs2017 amd64

00:09:20

passed #5777738
1809 windows docker
build vs2017 x86

00:09:38

 
  Test
passed #5777747
gstreamer
check fedora

00:07:15

passed #5777748
gstreamer
integration testsuites fedora 1/4

00:19:42

passed #5777749
gstreamer
integration testsuites fedora 2/4

00:18:49

passed #5777750
gstreamer
integration testsuites fedora 3/4

00:11:43

passed #5777751
gstreamer
integration testsuites fedora 4/4

00:19:56

passed #5777756
gstreamer
valgrind bad

00:09:01

passed #5777753
gstreamer
valgrind base

00:09:55

passed #5777752
gstreamer
valgrind core

00:15:48

passed #5777757
gstreamer
valgrind ges

00:09:03

passed #5777754
gstreamer
valgrind good

00:10:14

passed #5777755
gstreamer
valgrind ugly

00:04:47

 
  Integrate
passed #5777758
cross-android universal examples

00:10:30

passed #5777760
gst-ios-13.2
cross-ios universal examples

00:02:05

passed #5777759
documentation

00:22:28