Add Apache license header for V 5.0.0

[gzrp]

Add Apache license header for V 5.0.0

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 60.74%. Comparing base (9382aee) to head (864a26b).
Report is 38 commits behind head on dev-postgresql.

Additional details and impacted files

@@               Coverage Diff               @@
##           dev-postgresql    #1297   +/-   ##
===============================================
  Coverage           60.74%   60.74%           
===============================================
  Files                  85       85           
  Lines                4524     4524           
===============================================
  Hits                 2748     2748           
  Misses               1776     1776           

Flag	Coverage Δ
singa-cpp	60.74% <ø> (ø)

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