feat: add a fixed number of rows to take importing dataset from Hub

[jfcalvo]

Description

I have added a number of row to take importing a dataset from the hub. Specifically 500K rows. This can help us to avoid importing really big datasets with millions of rows into Argilla.

Refs argilla-io/roadmap#21

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested

• Manually tested importing a dataset with a big number of records (> 500K)

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 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 91.08%. Comparing base (f3e33bd) to head (15301f0).
Report is 4 commits behind head on feat/add-hub-dataset-import.

Files with missing lines	Patch %	Lines
argilla-server/src/argilla_server/jobs/hub_jobs.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@                       Coverage Diff                       @@
##           feat/add-hub-dataset-import    #5597      +/-   ##
===============================================================
+ Coverage                        91.05%   91.08%   +0.02%     
===============================================================
  Files                              150      150              
  Lines                             6204     6211       +7     
===============================================================
+ Hits                              5649     5657       +8     
+ Misses                             555      554       -1     

Flag	Coverage Δ
argilla-server	91.08% <50.00%> (+0.02%)	⬆️

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[burtenshaw]

@jfcalvo This should be changed to 10_000 for the first iteration.

cc @frascuchon