[backend] Add tests for importing Simulation (JSON) (#1489)

[antoinemzs]

Proposed changes

• Add tests for importing Simulation in JSON

Related issues

• Contributes to [ Unit testing - simulation scope ] - import/export of a simulation (JSON) #1489

Checklist

• I consider the submitted work as finished
• I tested the code for its functionality
• I wrote test cases for the relevant uses case
• I added/update the relevant documentation (either on github or on notion)
• Where necessary I refactored code to improve the overall quality
• For bug fix -> I implemented a test that covers the bug

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 12 lines in your changes missing coverage. Please review.

Project coverage is 35.91%. Comparing base (13d6e1b) to head (7f6d974).
Report is 32 commits behind head on release/current.

Files with missing lines	Patch %	Lines
...rc/main/java/io/openbas/rest/mapper/MapperApi.java	0.00%	4 Missing ⚠️
...main/java/io/openbas/importer/V1_DataImporter.java	72.72%	3 Missing ⚠️
...o/openbas/rest/exercise/service/ExportService.java	93.47%	2 Missing and 1 partial ⚠️
...rc/main/java/io/openbas/service/MapperService.java	0.00%	2 Missing ⚠️

Additional details and impacted files

@@                  Coverage Diff                  @@
##             release/current    #2219      +/-   ##
=====================================================
+ Coverage              33.73%   35.91%   +2.17%     
- Complexity              1566     1704     +138     
=====================================================
  Files                    583      587       +4     
  Lines                  18000    18481     +481     
  Branches                1168     1239      +71     
=====================================================
+ Hits                    6072     6637     +565     
+ Misses                 11635    11519     -116     
- Partials                 293      325      +32     

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