Use java.time.Duration rather than kotlin.time.Duration for Exporter config.

[JonathanLennox]

jitsi-metaconfig doesn't have support for the Kotlin class.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 48.02%. Comparing base (0360d04) to head (dc2b78a).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...in/kotlin/org/jitsi/videobridge/export/Exporter.kt	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #2383   +/-   ##
=========================================
  Coverage     48.02%   48.02%           
  Complexity     2712     2712           
=========================================
  Files           381      381           
  Lines         22074    22074           
  Branches       3351     3351           
=========================================
  Hits          10601    10601           
  Misses        10317    10317           
  Partials       1156     1156           

Files with missing lines	Coverage Δ
...in/kotlin/org/jitsi/videobridge/export/Exporter.kt	0.00% <0.00%> (ø)

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