[CODE HEALTH] Prevent std::out_of_range escaping noexcept substr callers

[denizariyan]

Fixes # (issue)

Changes

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[denizariyan]

I tried looking for context on why this was implemented like this in the git/pr history and it was added as part of a commit mentioning buffer overflow but this is not related to any buffer overflow. c9cbb1a

As far as I see there is no benefit of having a static string here, hence replaced with a str literal to prevent an additional bad_alloc potential on the same noexcept caller that was reported after fixing the other issue

[denizariyan]

I also chose not to mark this function noexcept (was marked initially in this PR). Since C++17 the exception specification is part of the function type, so adding it would change the type of a pre-existing public function without any benefits in this case

[codecov]

Codecov Report

❌ Patch coverage is 81.25000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.48%. Comparing base (e0e0458) to head (3271383).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
ext/src/http/client/curl/http_operation_curl.cc	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4562      +/-   ##
==========================================
+ Coverage   86.45%   86.48%   +0.03%     
==========================================
  Files         525      525              
  Lines       20450    20455       +5     
==========================================
+ Hits        17679    17689      +10     
+ Misses       2771     2766       -5     

Files with missing lines	Coverage Δ
api/include/opentelemetry/baggage/baggage.h	98.28% <100.00%> (ø)
api/include/opentelemetry/common/kv_properties.h	98.84% <100.00%> (-0.02%)	⬇️
api/include/opentelemetry/common/string_util.h	90.00% <100.00%> (+2.50%)	⬆️
...de/opentelemetry/trace/propagation/detail/string.h	93.34% <100.00%> (ø)
ext/src/http/client/curl/http_operation_curl.cc	61.16% <0.00%> (ø)

... and 3 files with indirect coverage changes

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