Use concurrent skiplist map for NettyRequest arguments

[justinlin-linkedin]

Summary

Map for header and query parameter in NettyRequest should be case-insensitive. Start using concurrent skiplist map with CASE_INSENSITIVE_ORDER from String.

Test

Added unit test

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.37%. Comparing base (52ba813) to head (a5dba9c).
Report is 125 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2927      +/-   ##
============================================
+ Coverage     64.24%   70.37%   +6.12%     
- Complexity    10398    11980    +1582     
============================================
  Files           840      864      +24     
  Lines         71755    73672    +1917     
  Branches       8611     8866     +255     
============================================
+ Hits          46099    51843    +5744     
+ Misses        23004    19133    -3871     
- Partials       2652     2696      +44     

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