[feature] Add loadBalancerClass support to proxy and pulsar CRDs

[SreedevT]

Summary

From the k8s docs:

    // loadBalancerClass is the class of the load balancer implementation this Service belongs to.
    // If specified, the value of this field must be a label-style identifier, with an optional prefix,
    // e.g. "internal-vip" or "example.com/internal-vip". Unprefixed names are reserved for end-users.
    // This field can only be set when the Service type is 'LoadBalancer'. If not set, the default load
    // balancer implementation is used, today this is typically done through the cloud provider integration,
    // but should apply for any default implementation. If set, it is assumed that a load balancer
    // implementation is watching for Services with a matching class. Any default load balancer
    // implementation (e.g. cloud providers) should ignore Services that set this field.
    // This field can only be set when creating or updating a Service to type 'LoadBalancer'.
    // Once set, it can not be changed. This field will be wiped when a service is updated to a non 'LoadBalancer' type.

AWS EKS uses this field on EKS clusters > 1.24 that have upgraded to the new AWS LoadBalancer Controller

Adds support for loadBalancerClass field in Proxy service configuration to resolve
Kubernetes validation error: "spec.loadBalancerClass: Invalid value: "null": may
not change once set".

Changes

• Added loadBalancerClass field to Proxy CRD and ServiceConfig model
• Modified service creation to only set loadBalancerClass when value is non-null
  (avoids Kubernetes validation error)
• Updated migration tool to preserve existing loadBalancerClass values
• Added comprehensive tests

Testing

• All existing tests pass
• New test testServiceLoadBalancerClassNull() verifies correct null handling
• Supports any load balancer class (MetalLB, AWS NLB, etc.)

Resolves the referenced issue #202 .

[SreedevT]

@pgier Could you take a look at this