refactor: move Enums to enums

[gabrielmbmb]

Description

This PR moves all the Enum classes of the Argilla server to the argilla.server.enums module in order to avoid circular imports, and to have one single file in which find all the enums (they are used across all the server codebase).

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
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I filled out the contributor form (see text above)
• I have added relevant notes to the CHANGELOG.md file (See https://keepachangelog.com/)

[alvarobartt]

LGTM, makes a lot of sense! My only concern is whether we should also include the V1 at the end of each Enum to differentiate v0 from v1 enums, or whether we should just split those in different modules, WDYT?

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: +0.60% 🎉

Comparison is base (6630d7b) 90.13% compared to head (eeadd92) 90.73%.
Report is 190 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3620      +/-   ##
===========================================
+ Coverage    90.13%   90.73%   +0.60%     
===========================================
  Files          233      261      +28     
  Lines        12493    13768    +1275     
===========================================
+ Hits         11261    12493    +1232     
- Misses        1232     1275      +43     

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