Feature request: Transition rules in spec.buckets[].lifecycle #279

Summary

Allow transition (and noncurrentVersionTransition) in bucket lifecycle rules of the Tenant CRD. This extends the lifecycle support added in #250 (requested in #249), which currently covers expiration and abortIncompleteMultipartUpload only.

Use Case

We run RustFS as the hot tier and move objects older than N days to a remote S3-compatible tier (Storj in our case; RustFS works with it since rustfs/rustfs#8363). The Tenant is deployed with Flux, and we want the transition rule declared in Git next to the rest of the bucket configuration.

Current Situation

• RustFS core supports Transition and NoncurrentVersionTransition in PutBucketLifecycleConfiguration, with StorageClass set to the name of a registered tier.
• The operator's lifecycle model has no transition, so such a rule cannot be expressed in the CRD.

Current Workaround

A Job that runs rc ilm rule add <alias>/<bucket> --transition-days N --storage-class <TIER> after the Tenant becomes ready. Problems:

• Imperative, outside the reconcile loop: no drift detection and no status on the Tenant.
• It cannot be combined with spec.buckets[].lifecycle. The operator owns the whole lifecycle document of a bucket, so the Job's rule and operator-managed rules would overwrite each other. Today we leave lifecycle unset on tiered buckets.

Request

spec:
  buckets:
    - name: main
      lifecycle:
        rules:
          - id: to-cold
            status: Enabled
            filter:
              prefix: ""
            transition:
              days: 1
              storageClass: COLD
            # optional, for versioned buckets:
            # noncurrentVersionTransition:
            #   noncurrentDays: 7
            #   storageClass: COLD

Points we think matter for the design

• The tier must already exist. RustFS rejects a lifecycle document whose StorageClass is not a registered tier. The operator could check GET /rustfs/admin/v3/tier before applying and report a clear condition on the bucket instead of a retry loop. The tier itself can be registered outside the operator; managing tiers in the CRD is a separate request (#).
• Validation. One Transition and one NoncurrentVersionTransition per rule, as RustFS enforces. days must be positive.
• Ownership. The existing canonical-XML ownership check and desired hash need to include the new elements, so a live document with a transition is not silently adopted or dropped.