[REFACTOR] argilla server: using pydantic v2

[frascuchon]

Description

An alternative work of pydantic v2 upgrade with the latest changes from develop.

The main problems I found:

• The Optional values are now required. This will affect how schemas are returned since default values are sets, including them as part of the schema result (record without responses or suggestions, for example)
• I found some serialization errors when the response body (an error) contains a ValueError object. The same is working with pydantic <2
• Automatic type conversion is not working anymore. This means that many client requests may fail ( values are not automatically converted to str, or some complex structures (record fields may be affected by this). We can still define custom model_validators, but we must apply them carefully.

Closes #4935

Refs #5508

Type of change

• Refactor (change restructuring the codebase without changing functionality)

How Has This Been Tested

Checklist

• I added relevant documentation
• I followed the style guidelines of this project
• I did a self-review of my code
• I made corresponding changes to the documentation
• I confirm 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

Attention: Patch coverage is 98.33333% with 6 lines in your changes missing coverage. Please review.

Project coverage is 91.77%. Comparing base (6e63b04) to head (4bd1522).
Report is 4 commits behind head on develop.

Files with missing lines	Patch %	Lines
...rver/src/argilla_server/api/schemas/v1/webhooks.py	93.33%	2 Missing ⚠️
...-server/src/argilla_server/errors/error_handler.py	93.33%	1 Missing ⚠️
argilla-server/src/argilla_server/jobs/hub_jobs.py	0.00%	1 Missing ⚠️
argilla-server/src/argilla_server/models/mixins.py	66.66%	1 Missing ⚠️
argilla-server/src/argilla_server/utils.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #5666      +/-   ##
===========================================
+ Coverage    91.55%   91.77%   +0.22%     
===========================================
  Files          165      161       -4     
  Lines         6675     6725      +50     
===========================================
+ Hits          6111     6172      +61     
+ Misses         564      553      -11     

Flag	Coverage Δ
argilla-server	91.77% <98.33%> (+0.22%)	⬆️

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[jfcalvo]

Masive effort! 💪