Bump mongoose version to accomodate MongoDB Atlas changes

[Naapperas]

MongoDB announced that Atlas would be migrating all database instances to version 7 of MongoDB.

This PR updates mongoose and the code accordingly to reflect the changes made (since this is potentially bumping 2 major versions).

There is no need to change the docker-compose.yaml file since it pulls from the untagged mongo image, aka, the latest image available on Docker Hub. I already checked and, on my machine, the image, when running mongosh, runs server version 7.x, which is what we want.

[render]

Your Render PR Server URL is https://nijobs-backend-pr-345.onrender.com.

Follow its progress at https://dashboard.render.com/web/srv-cmtdm8ta73kc73dqp60g.

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.27%. Comparing base (81bce7c) to head (0e594f0).
⚠️ Report is 2 commits behind head on develop.

Files with missing lines	Patch %	Lines
src/config/passport.js	77.77%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #345      +/-   ##
===========================================
- Coverage    90.33%   90.27%   -0.06%     
===========================================
  Files           54       54              
  Lines         1469     1471       +2     
  Branches       245      244       -1     
===========================================
+ Hits          1327     1328       +1     
- Misses         137      138       +1     
  Partials         5        5              

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[Naapperas]

Audit fails due to this, which was only reported 11 hours ago, will need to wait for a fix 💀