[Bug] Configuration accepts DRA capacity qualified names with multiple slashes

[junnhwan]

What happened

Kueue accepts a DRA consumable-capacity configuration whose sources[].capacity.name contains more than one slash, for example gpu.example.com/memory/bytes.

This field is documented as a Kubernetes DRA QualifiedName, which allows an optional DNS prefix and one name component separated by a single slash. The handwritten validation in pkg/config/validation.go splits the value and validates only the one-part and two-part cases; values with more than two parts fall through without an error.

What I expected to happen

Kueue should reject a capacity dimension name containing more than one slash during configuration validation.

How to reproduce it

Use a configuration with the DRA consumable-capacity feature enabled and a capacity source like:

featureGates:
  KueueDRAIntegrationConsumableCapacity: true
resources:
  deviceClassMappings:
  - name: gpu.memory
    deviceClassNames:
    - vgpu.example.com
    sources:
    - capacity:
        name: gpu.example.com/memory/bytes
        driver: gpu.example.com
        deviceSelector:
          cel:
            expression: device.driver == \gpu.example.com\\

At the current main revision, validateDeviceClassMappings accepts this value. It should return a validation error for the capacity name.

Proposed fix

Reject qualified names with more than one slash and add a regression test covering the invalid value.

AI tools were used to help investigate and draft this report. I reviewed the behavior, reproduction, and proposed fix.

[junnhwan]

/assign