docs: add svg converted png in docs for workaround pdf conversion issued from imagemagik

[lizable]

TL;DR

Updated image formats from SVG to PNG and added new icons for the documentation.

What changed?

• Converted several diagrams from SVG to PNG format, including server architecture, vfolder concepts, development setup, and run state diagrams.
• Added new icon images for various UI elements (e.g., arrows, social media icons, search).
• Included a new Backend.AI logo image.
• Updated references in RST files to point to the new PNG images instead of SVG files.

How to test?

1. Navigate to the documentation pages where diagrams are used.
2. Verify that all diagrams are displayed correctly in PNG format.
3. Check that the new icons appear properly in the documentation UI.
4. Ensure that the Backend.AI logo is visible and correctly formatted.

Why make this change?

This change improves compatibility and consistency across different browsers and devices. PNG format offers better support and rendering consistency compared to SVG, especially for complex diagrams. The addition of new icons enhances the visual appeal and usability of the documentation interface.

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Checklist: (if applicable)

• Milestone metadata specifying the target backport version
• Mention to the original issue
• Installer updates including:
  • Fixtures for db schema changes
  • New mandatory config options
• Update of end-to-end CLI integration tests in ai.backend.test
• API server-client counterparts (e.g., manager API -> client SDK)
• Test case(s) to:
  • Demonstrate the difference of before/after
  • Demonstrate the flow of abstract/conceptual models with a concrete implementation
• Documentation
  • Contents in the docs directory
  • docstrings in public interfaces and type annotations

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📚 Documentation preview 📚: https://sorna--2751.org.readthedocs.build/en/2751/

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📚 Documentation preview 📚: https://sorna-ko--2751.org.readthedocs.build/ko/2751/

[lizable]

• docs: add svg converted png in docs for workaround pdf conversion issued from imagemagik #2751 👈
• main

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