feat: Add loadBalancerClass attribute support for LoadBalancer services

[Copilot]

This PR adds support for the loadBalancerClass attribute on service.spec to enable Tailscale integration and other LoadBalancer class configurations.

Changes

• Added service.loadBalancerClass parameter to values.yaml with proper documentation comments
• Updated service template to conditionally include loadBalancerClass only when service type is LoadBalancer and the value is defined
• Added comprehensive test coverage with 3 new test cases covering all scenarios:
  • LoadBalancer service with loadBalancerClass defined
  • Non-LoadBalancer service with loadBalancerClass defined (should be omitted)
  • LoadBalancer service without loadBalancerClass defined (should be omitted)
• Updated README.md documentation with the new service parameter

Behavior

The loadBalancerClass field follows the same pattern as existing LoadBalancer-specific fields like loadBalancerIP and loadBalancerSourceRanges:

• Only applied when service.type is "LoadBalancer"
• Omitted when not defined or when service type is not LoadBalancer
• Allows users to specify custom LoadBalancer implementations like Tailscale

Example Usage

service:
  enabled: true
  type: LoadBalancer
  loadBalancerClass: tailscale
  annotations:
    tailscale.com/hostname: myapp-host
  ports:
    - name: http
      port: 80
      targetPort: 8080

This generates a service with spec.loadBalancerClass: tailscale as required for Tailscale integration.

All existing tests continue to pass, and the new functionality is fully tested with 211 total tests passing.

Fixes #428.

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[jr200]

looks good!