Upgrade analytics event publisher client to 1.2.20

[HeshanSudarshana]

This PR upgrades the analytics event publisher client to 1.2.20.

Related PR: wso2/apim-analytics-publisher#115

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 12.02%. Comparing base (f7c254e) to head (e7d526d).
Report is 7 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #13560      +/-   ##
============================================
- Coverage     14.57%   12.02%   -2.56%     
+ Complexity      700      618      -82     
============================================
  Files           255      255              
  Lines         11682    11682              
  Branches       1223     1223              
============================================
- Hits           1703     1405     -298     
- Misses         9955    10260     +305     
+ Partials         24       17       -7     

Flag	Coverage Δ
integration_tests	12.02% <ø> (-2.56%)	⬇️

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