Add Backblaze B2 cloud storage provider support

[jeronimodeleon]

Motivation and context

This change adds support for Backblaze B2 as a cloud storage provider in CVAT. B2 is a cost-effective S3-compatible cloud storage solution that provides an alternative to other cloud storage providers.

This enhancement enables users to:

• Connect their B2 buckets to CVAT for dataset storage
• Leverage B2's competitive pricing for cloud storage
• Use B2's S3-compatible API for seamless integration

Key features implemented:

• Full S3-compatible API integration via BackblazeB2 class
• Complete CRUD operations (upload, download, list, delete)
• Custom telemetry with B2-specific user-agent and event logging
• Flexible endpoint URL configuration for different B2 regions
• UI integration with provider dropdown, icon, and form fields

Technical changes:

Backend:

• Added BackblazeB2 class in cloud_provider.py extending AWS_S3
• Added BACKBLAZE_B2 to CloudProviderChoice enum
• Updated serializers to handle B2-specific attributes
• Code formatted with black and isort

Frontend:

• Added BackblazeB2Provider icon component with proper spacing
• Added B2 to provider selection and filter components
• Added B2 logo asset

Documentation:

• Complete B2 setup guide in attach-cloud-storage.md
• Updated cloud-storages.md with B2 provider information

How has this been tested?

• Added test_can_create_backblaze_b2_cloud_storage test case to verify B2 cloud storage creation
• Added B2 fixtures in test data
• Tested CRUD operations (create, read, update, delete) with B2 buckets
• Verified UI components render correctly with B2 provider selection
• Confirmed S3-compatible API integration works with B2 endpoints
• Validated custom telemetry and user-agent headers

Checklist

• I submit my changes into the develop branch
• I have created a changelog fragment
• I have updated the documentation accordingly
• I have added tests to cover my changes
• I have linked related issues

License

• I submit my code changes under the same MIT License that covers the project.

[nmanovic]

@jeronimodeleon , thank you for the PR. Unfortunately, we cannot accept it. Feel free to contact us here: https://www.cvat.ai/contact (General Inquiries). I will explain my point and also discuss possible ways to move forward with the PR.

[SpecLad]

It's already possible to use B2 via their S3-compatible API; you just need to select S3 as the provider, and set a custom endpoint URL. As such, I don't think we need to add any dedicated code for this, although maybe a mention in the documentation could be useful. Either way, please talk to @nmanovic first.

[sonarqubecloud]

Quality Gate passed

Issues
15 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
1.0% Duplication on New Code

See analysis details on SonarQube Cloud