Add gst_video_sync integration test

[mvollrath]

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[sourcelevel-bot[bot]]

SourceLevel has finished reviewing this Pull Request and has found:

• 416 possible new issues (including those that may have been commented here).
• 189 fixed issues! 🎉

But beware that this branch is 41 commits behind the EndPointCorp:master branch, and a review of an up to date branch would produce more accurate results.

You can see more details about this review at https://app.sourcelevel.io/github/EndPointCorp/lg_ros_nodes/pulls/408.