feat(apache): support check license header with RAT

[imbajin]

use mvn apache-rat:check to see the report, and use find ./ -name rat.txt -print0 | xargs -0 -I file cat file > merged-rat.txt to merge all modules' check file

and fix current license problems

TODO: we should add & use apache-rat plugin in other repos later

BTW, we'd reuse such configs better (rather than copy them in each repo)

[codecov[bot]]

Codecov Report

Merging #108 (1318ae0) into master (e85ab38) will not change coverage. The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #108   +/-   ##
=========================================
  Coverage     93.15%   93.15%           
  Complexity       65       65           
=========================================
  Files             9        9           
  Lines           263      263           
  Branches         22       22           
=========================================
  Hits            245      245           
  Misses            8        8           
  Partials         10       10           

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