feat: progress report for image pulling

[fregataa]

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

[fregataa]

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• feat: progress report for image pulling #2728 👈 (View in Graphite)
• chore: Add sub-progress reporter #2727
• feat: Add CREATING status to compute session and kernel #3114
• feat: Implement check-and-pull mechanism for session creation lifecycle #2721 : 1 other dependent PR (#3127 )
• feat: Add check-and-pull RPC function  #2692
• chore: Clean-up parameters of bulk_get_image_configs() #3102
• main

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