[backend] fix code coverage

[labo-flg]

This PR fixes code coverage (all credits to @richard-julien 🙌)

The plugin vitestMigrationPlugin was turning the global pattern *.js in database/migration.js into real JS code, introducing several lines into the code. However, the resulting source mapping was not updated.

This introduced a shift in the code base as displayed in the coverage reports.

We are not testing migrations scripts, so we can safely turn of this plugin. This meant refactoring the initialization phase so that vitest won't ever import migration.js during test setup.

I've added a small change to the test base to check for coverage improvement, and reporting on the right lines of code.

This is working properly:

[codecov]

Codecov Report

Attention: 497 lines in your changes are missing coverage. Please review.

Comparison is base (605eb54) 66.14% compared to head (bafc094) 64.78%.
Report is 3 commits behind head on master.

Files	Patch %	Lines
...pencti-graphql/src/database/data-initialization.js	0.00%	254 Missing ⚠️
opencti-platform/opencti-graphql/src/managers.js	0.00%	221 Missing ⚠️
...ti-platform/opencti-graphql/src/database/engine.js	29.41%	12 Missing ⚠️
...cti-platform/opencti-graphql/src/initialization.js	0.00%	5 Missing ⚠️
...-platform/opencti-graphql/src/database/rabbitmq.js	40.00%	3 Missing ⚠️
opencti-platform/opencti-graphql/src/boot.js	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5748      +/-   ##
==========================================
- Coverage   66.14%   64.78%   -1.37%     
==========================================
  Files         513      515       +2     
  Lines       60805    60815      +10     
  Branches     4447     4849     +402     
==========================================
- Hits        40220    39398     -822     
- Misses      20585    21417     +832     

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