feat(cas-backend): add configurable max blob size per backend

[migmartri]

Summary

This PR adds the ability to configure maximum blob size for CAS backends dynamically through API and CLI, replacing the static Helm chart configuration.

chainloop cas-backend update azure-blob --name new-blob --max-bytes 2.5G

┌──────────┬────────────────────────┬───────────┬─────────────┬───────────────┬─────────┬────────────────────────────────────────────────────┐
│ NAME     │ LOCATION               │ PROVIDER  │ DESCRIPTION │ LIMITS        │ DEFAULT │ STATUS                                             │
├──────────┼────────────────────────┼───────────┼─────────────┼───────────────┼─────────┼────────────────────────────────────────────────────┤
│ new-blob │ chainloop/integrations │ AzureBlob │             │ MaxSize: 2.5G │ false   │ invalid                                            │
│          │                        │           │             │               │         │ Failed to access CAS backend credentials in extern │
│          │                        │           │             │               │         │ al Secrets Manager                                 │
└──────────┴────────────────────────┴───────────┴─────────────┴───────────────┴─────────┴────────────────────────────────────────────────────┘

Changes

• API Layer: Added optional max_bytes field to CASBackend Create/Update requests with buf validation (10MB minimum)
• Business Logic:
  • Enforces 10MB minimum for all backends
  • Prevents inline backends from having their max_bytes updated (they use fixed 500KB limit)
  • Uses provided value or falls back to system default (100MB)
• CLI:
  • Added --max-bytes as persistent flag on parent add and update commands
  • Supports human-readable formats (e.g., 100MB, 1GB)
  • Client-side validation removed (server-side only)
• Tests: Updated integration tests to handle new optional parameter

API Examples

Create backend with custom max size

chainloop cas-backend add aws-s3 --name my-backend --bucket my-bucket \
  --access-key-id XXX --secret-access-key YYY --region us-east-1 \
  --max-bytes 500MB

Update backend max size

chainloop cas-backend update aws-s3 --name my-backend --max-bytes 1GB

Validation

• Minimum size: 10MB (enforced at API level via buf validation and business logic)
• Inline backends: Cannot update max_bytes (returns validation error)
• Format: Supports human-readable byte formats via bytefmt library