feat: Relax the health checks for STUN

[bgrozev]

By default only fail when there is no valid address for ICE. Put the
option to require STUN behind a flag.

[codecov]

Codecov Report

Attention: 9 lines in your changes are missing coverage. Please review.

Comparison is base (719465d) 43.98% compared to head (207ad1f) 43.98%.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2077      +/-   ##
============================================
- Coverage     43.98%   43.98%   -0.01%     
+ Complexity     1918     1917       -1     
============================================
  Files           340      340              
  Lines         18881    18895      +14     
  Branches       2593     2595       +2     
============================================
+ Hits           8305     8311       +6     
- Misses         9724     9732       +8     
  Partials        852      852              

Files	Coverage Δ
...rg/jitsi/videobridge/health/config/HealthConfig.kt	100.00% <100.00%> (ø)
...n/org/jitsi/videobridge/health/JvbHealthChecker.kt	34.78% <0.00%> (-18.56%)	⬇️

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