front: add lazy loader message on GET in stdcm

[clarani]

closes #8610

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 0% with 25 lines in your changes missing coverage. Please review.

Project coverage is 37.83%. Comparing base (b4b2d7f) to head (9cde509).
Report is 3 commits behind head on dev.

Files with missing lines	Patch %	Lines
...ications/stdcm/hooks/useProjectedTrainsForStdcm.ts	0.00%	8 Missing ⚠️
...WithSpaceTimeChart/ManchetteWithSpaceTimeChart.tsx	0.00%	6 Missing ⚠️
...ations/operationalStudies/hooks/useScenarioData.ts	0.00%	4 Missing ⚠️
...tdcm/components/StdcmResults/StdcmDebugResults.tsx	0.00%	4 Missing ⚠️
...nalStudies/components/Scenario/ScenarioContent.tsx	0.00%	2 Missing ⚠️
...ons/operationalStudies/views/SimulationResults.tsx	0.00%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #9490      +/-   ##
==========================================
- Coverage   37.84%   37.83%   -0.02%     
==========================================
  Files         990      990              
  Lines       90921    90929       +8     
  Branches     1176     1176              
==========================================
- Hits        34412    34401      -11     
- Misses      56055    56074      +19     
  Partials      454      454              

Flag	Coverage Δ
editoast	73.23% <ø> (-0.04%)	⬇️
front	20.11% <0.00%> (-0.01%)	⬇️
gateway	2.18% <ø> (ø)
osrdyne	3.28% <ø> (ø)
railjson_generator	87.49% <ø> (ø)
tests	86.74% <ø> (ø)

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[SharglutDev]

Lgtm and tested, good job ! Left just one suggestion, you can resolve yourself after treating it or not :)