editoast: use 'const' syntax from 'tracing' for opentelemetry semantic convention

[woshilapin]

We can actually use variables as keys in span metadata, as long as they're const. See the documentation.

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 62.50000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 79.80%. Comparing base (844c6b3) to head (5f8e62c).
Report is 11 commits behind head on dev.

Files with missing lines	Patch %	Lines
.../src/db_connection_pool/tracing_instrumentation.rs	62.50%	3 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##              dev   #10110      +/-   ##
==========================================
- Coverage   79.81%   79.80%   -0.02%     
==========================================
  Files        1053     1053              
  Lines      105483   105483              
  Branches      727      727              
==========================================
- Hits        84196    84182      -14     
- Misses      21245    21259      +14     
  Partials       42       42              

Flag	Coverage Δ
editoast	73.70% <62.50%> (-0.05%)	⬇️
front	89.13% <ø> (ø)
gateway	2.18% <ø> (ø)
osrdyne	3.28% <ø> (ø)
railjson_generator	87.50% <ø> (ø)
tests	87.00% <ø> (ø)

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[emersion]

Nice!

[hamz2a]

Thanks!

[leovalais]

Much better!