Enhancement: Add strict format validation for yurthub storage keys

[mohammd-khalil]

What type of PR is this?

/kind enhancement
/sig storage

What this PR does / why we need it:

ValidateKey in pkg/yurthub/storage/utils/validate.go currently only checks
that a storage.Key is non-nil/non-empty and has the expected concrete Go
type (via reflect.TypeOf). It does not validate the internal format of the
key's path, as noted by an existing TODO comment:

// TODO: should also valid the key format

This means a key with the correct type but a malformed internal path (e.g.
missing segments, invalid resource/version/group format) passes validation
silently, and only fails later when it is actually parsed/used (e.g. by
disk.ExtractKeyBuildInfo).

This PR completes the TODO by:

• Adding an optional KeyFormatValidator interface (Validate() error) in
  pkg/yurthub/storage, kept separate from the existing minimal Key
  interface so it stays backward compatible for key types that don't need
  format validation (e.g. ClusterInfoKey).
• Implementing Validate() on disk.storageKey, reusing the same parsing
  rules already used by ExtractKeyBuildInfo.
• Updating ValidateKey in utils/validate.go to call Validate() via a
  type assertion, only when the key implements it.
• Adding unit tests covering both disk.storageKey.Validate() and the
  updated utils.ValidateKey.

Which issue(s) this PR fixes:

Fixes #2775

Special notes for your reviewer:

• Key interface itself (Key() string) was left unchanged; KeyFormatValidator
  is an additive, opt-in interface, so no existing implementation is broken.
• etcd storage key was not modified in this PR since its key format/needs
  weren't covered — happy to follow up separately if a similar check is
  wanted there.

Does this PR introduce a user-facing change?

NONE

other Note

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

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

See analysis details on SonarQube Cloud