Allow passing a per-request minInterval to RateLimit.

[JonathanLennox]

Add more tests for RateLimit.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 42.73%. Comparing base (9a35a58) to head (ca6cd98).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #152   +/-   ##
=========================================
  Coverage     42.73%   42.73%           
  Complexity      276      276           
=========================================
  Files            60       60           
  Lines          2506     2506           
  Branches        348      348           
=========================================
  Hits           1071     1071           
  Misses         1354     1354           
  Partials         81       81           

Files with missing lines	Coverage Δ
src/main/kotlin/org/jitsi/utils/RateLimit.kt	100.00% <100.00%> (ø)

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