[FEATURE] Support putFragmentMetadata from kvssink

[niyatim23]

Issue #, if available:
#1031

What was changed?
Modify kvssink and sample application to support adding metadata per fragment

Why was it changed?
This feature was missing from kvssink and was requested by multiple customers

How was it changed?

• This feature allows adding multiple metadata tags to fragments until a limit (10 metadata per fragment) is reached. To repeatedly put the metadata while streaming, a timer has been used which triggers a function put-metadata every 2 seconds. This application-level logic can be customized by the customers to be fired on their own set of events / frequency. put-metadata can be modified by the customers to generate metadata tags to be put. Currently, they consume values from a global instance of CustomData whose counter is updated within put-metadata itself. put-metadata also calls put-fragment-metadata
• put-fragment-metadata generates the GstStructure expected by the GST_EVENT_CUSTOM_DOWNSTREAM and ultimately triggers the GST_EVENT_CUSTOM_DOWNSTREAM that handles the tags and calls the underlying KVS API putFragmentMetadata.
• When this event is triggered, it checks whether the structure is in the expected format. If it has, it warns the customer about it through the logs without disrupting the streaming.

What testing was done for the changes?
Tested the following locally:

• Tested that the metadata was persisted in the video by checking the video dump with mkvinfo
• Tested that the metadata marked as persistent is indeed persisted for each fragment of the video
• Tested that the metadata marked as non-persistent is not persisted for each fragment of the video
• Tested that the metadata that is to be put, toggles between persistent and non-persistent and the both of them are marked correctly in the video
• Tested that the streaming continues despite failures in the putFragmentMetadata
• Tested that sending empty values for persistent metadata removes it
• mkvinfo on a video dump from the tests (even metadata-keys are persistent, odd ones are non-persistent): mkvinfo-metadata.txt

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 58 lines in your changes are missing coverage. Please review.

Project coverage is 16.27%. Comparing base (eeb392f) to head (db6d18f).
Report is 9 commits behind head on develop.

❗ Current head db6d18f differs from pull request most recent head 47d702d. Consider uploading reports for the commit 47d702d to get more accurate results

Files	Patch %	Lines
samples/kvssink_gstreamer_sample.cpp	0.00%	50 Missing ⚠️
src/gstreamer/gstkvssink.cpp	0.00%	8 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1122      +/-   ##
===========================================
- Coverage    16.48%   16.27%   -0.22%     
===========================================
  Files           50       50              
  Lines         7019     7092      +73     
===========================================
- Hits          1157     1154       -3     
- Misses        5862     5938      +76     

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[hassanctech]

LGTM

[hassanctech]

lgtm