feat: improve HubDataset image processing support

[jfcalvo]

Description

This PR adds the following changes related to how HubDataset import functionality process rows with images:

• If the image has not format we transform the image to png.
• We convert images to RGB color space to avoid problems with other unsupported color spaces.

Refs argilla-io/roadmap#21

Type of change

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

How Has This Been Tested

• Manually testing microsoft/cats_vs_dogs dataset.

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 ✅

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Additional details and impacted files

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Flag	Coverage Δ
argilla-server	91.15% <100.00%> (?)

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