feat: use different database for unit tests

[gabrielmbmb]

Description

I've updated the unit test setup to use a different database than the one used by the local deployment of the Argilla server. In addition, I've updated the pytest fixtures that provided a connection to the DB, and now before executing every test a new transaction is created that gets rollbacked when the execution of the test has finished, leaving no traces in the DB.

Also, I've aligned the SQLAlchemy models metadata with the metadata in the current alembic migrations scripts.

Closes #2987

Type of change

• New feature (non-breaking change which adds functionality)
• Refactor (change restructuring the codebase without changing functionality)
• Improvement (change adding some improvement to an existing functionality)

How Has This Been Tested

All the unit tests are passing using this new DB for the tests.

Checklist

• I have merged the original branch into my forked branch
• I added relevant documentation
• follows the style guidelines of this project
• I did a self-review of my code
• I made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have added relevant notes to the CHANGELOG.md file (See https://keepachangelog.com/)

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.03 ⚠️

Comparison is base (7866ee4) 92.90% compared to head (93b1487) 92.87%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2993      +/-   ##
===========================================
- Coverage    92.90%   92.87%   -0.03%     
===========================================
  Files          204      204              
  Lines        10793    10799       +6     
===========================================
+ Hits         10027    10030       +3     
- Misses         766      769       +3     

Flag	Coverage Δ
pytest	92.87% <100.00%> (-0.03%)	⬇️

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

Impacted Files	Coverage Δ
src/argilla/__main__.py	100.00% <100.00%> (ø)
src/argilla/server/commons/telemetry.py	89.09% <100.00%> (-0.20%)	⬇️
src/argilla/server/database.py	92.30% <100.00%> (+0.30%)	⬆️
src/argilla/server/models/models.py	97.82% <100.00%> (+0.09%)	⬆️
src/argilla/tasks/__init__.py	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

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[frascuchon]

super nice!