feat: Add ping to the exporter.'

[bgrozev]

• feat: Add ping/pong to exporter.
• feat: Use MediaJson, match ping/pong IDs.
• squash: Fix ping timeout.

[codecov]

Codecov Report

❌ Patch coverage is 5.55556% with 17 lines in your changes missing coverage. Please review.
✅ Project coverage is 48.02%. Comparing base (d73cf53) to head (367ae52).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...in/kotlin/org/jitsi/videobridge/export/Exporter.kt	0.00%	17 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2379      +/-   ##
============================================
- Coverage     48.06%   48.02%   -0.04%     
+ Complexity     2716     2712       -4     
============================================
  Files           381      381              
  Lines         22057    22064       +7     
  Branches       3348     3348              
============================================
- Hits          10602    10597       -5     
- Misses        10301    10311      +10     
- Partials       1154     1156       +2     

Files with missing lines	Coverage Δ
...rc/main/java/org/jitsi/videobridge/Conference.java	24.15% <ø> (ø)
...in/org/jitsi/videobridge/export/ExporterWrapper.kt	12.82% <100.00%> (ø)
...in/kotlin/org/jitsi/videobridge/export/Exporter.kt	0.00% <0.00%> (ø)

... and 1 file with indirect coverage changes

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