Simplify tracing-grpc example

[utpilla]

Changes

• Users can simply pass a &str instead of a String
• Users don't have to create a Vec and pass an array

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.6%. Comparing base (3e49f23) to head (cefbcf0).

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #1886   +/-   ##
=====================================
  Coverage   74.6%   74.6%           
=====================================
  Files        122     122           
  Lines      19952   19952           
=====================================
+ Hits       14901   14902    +1     
+ Misses      5051    5050    -1     

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