Add JuiceFS WebDAV server support

[Copilot]

Adds a new WebDAV CRD that manages a JuiceFS WebDAV server deployment, exposing a JuiceFS filesystem over the WebDAV protocol via a Kubernetes Deployment + Service.

New API

apiVersion: juicefs.io/v1
kind: WebDAV
metadata:
  name: webdav-example
spec:
  image: juicedata/mount:ee-5.3.6-c8ec652
  replicas: 1
  secretRef:
    name: juicefs-secret   # same secret format as CacheGroup
  port: 9007               # default
  serviceType: ClusterIP   # default
  options:
    - gzip

Key design decisions

• EE mode (secret contains name + token): runs juicefs auth <volume> then exec juicefs webdav <volume> 0.0.0.0:<port>
• CE mode (secret contains metaurl): skips auth, runs exec juicefs webdav <metaurl> 0.0.0.0:<port> directly; env-var injection for stripped secrets is skipped to avoid missing-key pod failures
• Reuses shared secret parsing infrastructure (secretKeys, secretStrippedEnvs, initconfig) from the CacheGroup builder
• Status tracks Pending / Progressing / Ready phases derived from Deployment.Status.ReadyReplicas

Changes

• api/v1/webdav_types.go — WebDAV / WebDAVList CRD schema; short name wdav
• api/v1/zz_generated.deepcopy.go — generated DeepCopy methods
• pkg/builder/webdav.go — WebDAVBuilder: generates Deployment and Service
• pkg/builder/webdav_test.go — 12 unit tests covering EE/CE modes, option parsing, Deployment/Service generation
• internal/controller/webdav_controller.go — reconciler managing Deployment + Service lifecycle and status sync
• cmd/app/controller.go — registers WebDAVReconciler
• pkg/common/common.go — KindWebDAV, LabelWebDAV, LabelWebDAVValue, MaxWebDAVConcurrentReconciles, GenWebDAVName
• config/crd/bases/juicefs.io_webdavs.yaml — generated CRD manifest (via make manifests)
• config/rbac/role.yaml — auto-generated RBAC rules for webdavs resources