editoast: Add mvt_view_metadata() route to editoast

[bloussou]

This PR is :

• adding /layers/layer/{layer_slug}/mvt/{view_slug}/ route to editoast
• adding max_zoom field to map_layers.yml

close #2890

[codecov]

Codecov Report

Merging #2912 (e74485e) into dev (12ec135) will increase coverage by 0.05%.
The diff coverage is 83.33%.

❗ Current head e74485e differs from pull request most recent head e7e6cf6. Consider uploading reports for the commit e7e6cf6 to get more accurate results

@@             Coverage Diff              @@
##                dev    #2912      +/-   ##
============================================
+ Coverage     38.07%   38.13%   +0.05%     
  Complexity     1713     1713              
============================================
  Files           598      599       +1     
  Lines         18207    18229      +22     
  Branches       2513     2513              
============================================
+ Hits           6933     6951      +18     
- Misses        10868    10872       +4     
  Partials        406      406              

Flag	Coverage Δ
editoast	73.37% <83.33%> (+0.08%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
editoast/src/chartos/map_layers.rs	100.00% <ø> (ø)
editoast/src/client/mod.rs	100.00% <ø> (ø)
editoast/src/views/layers/layer.rs	78.94% <78.94%> (ø)
editoast/src/main.rs	35.48% <100.00%> (+2.15%)	⬆️
editoast/src/views/layers/mod.rs	100.00% <100.00%> (ø)

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[bloussou]

Last commit e74485e is a suggestion to avoid unpredictable order in response : https://github.com/DGEXSolutions/osrd/actions/runs/3949537955/jobs/6760877075#step:10:405

The suggestion was taken from rust-lang/rfcs#2731

I can revert it and find another way if you are not ok with this