[stable4.7] fix(freebusy): free busy ignoring user's time zone

[st3iny]

Manual backport of #6665

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 15.51%. Comparing base (c408814) to head (7b2cca9).
Report is 1 commits behind head on stable4.7.

Additional details and impacted files

@@            Coverage Diff             @@
##           stable4.7    #6673   +/-   ##
==========================================
  Coverage      15.51%   15.51%           
==========================================
  Files            206      206           
  Lines           9257     9257           
  Branches        1931     1931           
==========================================
  Hits            1436     1436           
  Misses          7821     7821           

Flag	Coverage Δ
javascript	15.51% <ø> (ø)

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