Add k8s.get operation for retrieving resources and extracting fields

[Cali0707]

Description

Add a k8s.get operation to retrieve Kubernetes resources and extract specific fields. This is the most commonly needed operation across the mcpchecker kube-mcp-server example tasks, required by 8+ tasks for verification purposes.

Current bash tasks use patterns like:

• kubectl get deployment web-app -o jsonpath='{.status.availableReplicas}'
• kubectl get pods -l app=nginx -o jsonpath='{.items[0].status.containerStatuses[0].restartCount}'
• kubectl get pvc storage-pvc -o jsonpath='{.spec.volumeName}'

Requirements

• Support retrieving a single resource by name and namespace
• Support retrieving resources by label selector
• Support an expect block for inline verification (similar to HTTP step pattern)
• Return resource data in outputs for potential use in subsequent steps (output referencing is handled separately)

Example Usage

Inline verification with expect:

- k8s.get:
    apiVersion: apps/v1
    kind: Deployment
    metadata:
      name: web-app
      namespace: scale-test
    expect:
      fields:
        - path: status.availableReplicas
          equals: 2

Acceptance Criteria

• Can retrieve a resource by apiVersion, kind, name, and namespace
• Can filter resources using label selectors
• Supports expect.fields for inline field assertions (path, equals, type, match, exists)
• Handles not-found errors gracefully
• Operation is documented in extension manifest