Add OSS attribution to LICENSE.txt

[liry]

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[ghost]

Build succeeded (check pipeline).

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.11%. Comparing base (2fc7720) to head (6bd1f03).
⚠️ Report is 92 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #1147   +/-   ##
=========================================
  Coverage     83.11%   83.11%           
  Complexity     2615     2615           
=========================================
  Files           346      346           
  Lines          6705     6705           
  Branches        482      482           
=========================================
  Hits           5573     5573           
  Misses          934      934           
  Partials        198      198           

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[ghost]

Build succeeded (gate pipeline).

• https://checklist.intgdc.com/job/compliance/job/gooddata-java-merge-compliance-check/291/ : SUCCESS in 27s
• https://checklist.intgdc.com/job/compliance/job/gooddata-java-fossa-scanning-zuul-el7/129/ : FAILURE in 2m 47s (non-voting)