Feat: add call option for routing region & zone

[pulkit4tech]

• Description and context for reviewers: one partner, one stranger

RELEASE NOTES:

• add call option for routing region & zone

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.67%. Comparing base (d8dd9f2) to head (67bed02).

Additional details and impacted files

@@                        Coverage Diff                        @@
##           add-crosszone-header-for-grpc    #2391      +/-   ##
=================================================================
+ Coverage                          84.65%   84.67%   +0.01%     
=================================================================
  Files                                276      276              
  Lines                              16122    16140      +18     
=================================================================
+ Hits                               13648    13666      +18     
  Misses                              2024     2024              
  Partials                             450      450              

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