Add simpler kvssink sample

[stefankiesz]

Adds a new kvsink sample that allows for simple configuration with command line arguments and defaults to video-only, videotestsrc stream.

Minor fixes in existing kvssink sample.

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[codecov-commenter]

Codecov Report

Attention: 278 lines in your changes are missing coverage. Please review.

Comparison is base (6af9a7a) 16.38% compared to head (4b5870b) 15.74%.
Report is 1 commits behind head on develop.

❗ Current head 4b5870b differs from pull request most recent head d20a69d. Consider uploading reports for the commit d20a69d to get more accurate results

Files	Patch %	Lines
samples/kvssink_simple_sample.cpp	0.00%	272 Missing ⚠️
src/gstreamer/gstkvssink.cpp	0.00%	6 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1121      +/-   ##
===========================================
- Coverage    16.38%   15.74%   -0.64%     
===========================================
  Files           51       52       +1     
  Lines         6849     7126     +277     
===========================================
  Hits          1122     1122              
- Misses        5727     6004     +277     

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