chore: move webhooks folder outside api folder

[jfcalvo]

Description

As discussed this PR is moving webhooks folder outside api folder. Now that we have specific schemas for webhooks it does not have much sense to have this code inside the api folder.

Refs #1836

Type of change

• Refactor (change restructuring the codebase without changing functionality)

How Has This Been Tested

• Running test suite.

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

All modified and coverable lines are covered by tests ✅

Project coverage is 91.40%. Comparing base (48a0dfe) to head (6d9c6da).
Report is 1 commits behind head on feat/add-webhooks-feature-branch.

Additional details and impacted files

@@                         Coverage Diff                          @@
##           feat/add-webhooks-feature-branch    #5493      +/-   ##
====================================================================
- Coverage                             91.42%   91.40%   -0.02%     
====================================================================
  Files                                   157      157              
  Lines                                  6321     6321              
====================================================================
- Hits                                   5779     5778       -1     
- Misses                                  542      543       +1     

Flag	Coverage Δ
argilla-server	91.40% <100.00%> (-0.02%)	⬇️

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