Use tracing's pretty formatter for editoast logs

[leovalais]

Configures tracing formatter to pretty to improve log readability. This is especially valuable for multiline log entries. Likewise, the span contexts output is more readable (one line per span instead of joining them using : for the compact formatter).

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 29.38%. Comparing base (4bdd9b5) to head (74bd195).
Report is 3 commits behind head on dev.

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Additional details and impacted files

@@            Coverage Diff            @@
##                dev    #7548   +/-   ##
=========================================
  Coverage     29.37%   29.38%           
  Complexity     2014     2014           
=========================================
  Files          1200     1200           
  Lines        147411   147488   +77     
  Branches       2893     2894    +1     
=========================================
+ Hits          43303    43337   +34     
- Misses       102405   102447   +42     
- Partials       1703     1704    +1     

Flag	Coverage Δ
core	75.06% <ø> (-0.01%)	⬇️
editoast	72.46% <ø> (-0.08%)	⬇️
front	9.76% <ø> (ø)
gateway	2.41% <ø> (ø)
railjson_generator	87.49% <ø> (ø)
tests	71.78% <ø> (ø)

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[leovalais]

Thanks for the approve! Since this change is a bit opinionated, I'll wait before merging maybe until the end of the week to let someone who would be strongly opinionated against that speak out.