feat: add Azure Blob Storage support with Workload Identity and S3 backward compatibility

[raphaelquati]

Summary

This PR adds native Azure Blob Storage support to core-dump-handler while preserving existing S3 behavior.

What is included

• Agent storage backend abstraction with:

  • S3 backend (existing behavior)
  • Azure Blob backend (new)

• Azure authentication flow:

  • Managed Identity / Workload Identity first
  • Connection string/account key as fallback

• Helm chart updates:

  • Azure-related values and environment wiring
  • Workload Identity labels/annotations support
  • Optional provider auto-detection support

• Documentation updates:

  • Azure deployment examples
  • Workload Identity guidance

Backward compatibility

• S3 remains supported and unchanged for current users
• Azure path is opt-in via Azure configuration
• No breaking change intended for existing S3 deployments

Validation

Validated end-to-end on AKS:

• Core dump was generated and collected
• Upload to Azure Blob returned HTTP 201
• Uploaded blob was listed and verified in the target container

Related issue

Refs #74 #164

[raphaelquati]

Validated end-to-end on AKS with Azure Workload Identity; upload succeeded with HTTP 201 and blob presence confirmed in the target container.