Add support for internal service specific labels
Fixes #12428

Description
This PR adds the ability to specify labels specifically for the internal ingress-nginx service without affecting the main controller service. This is particularly useful for use cases like external-dns configuration where labels need to be set only on the internal service.

Changes

• Modified templates/controller-service-internal.yaml to support internal-specific labels
• Removed mandatory annotations requirement for internal service
• Fixed indentation in templates/controller-deployment.yaml
• Added test case for internal service labels

Code Changes

1. Added support for internal-specific labels:

 labels:
    {{- include "ingress-nginx.labels" . | nindent 4 }}
    app.kubernetes.io/component: controller
  {{- if .Values.controller.service.internal.labels }}
    {{- toYaml .Values.controller.service.internal.labels | nindent 4 }}
  {{- end }}

2. Removed mandatory annotations requirement:

From

{{- if and .Values.controller.service.enabled .Values.controller.service.internal.enabled .Values.controller.service.internal.annotations -}}

To

{{- if and .Values.controller.service.enabled .Values.controller.service.internal.enabled -}}

Testing Performed
Tested the following scenarios:

1. Adding custom labels to internal service only
2. Verifying label isolation (labels on internal service don't appear on main service)
3. Creating internal service without requiring annotations
4. Confirming template renders correctly

Test configuration added in:
charts/ingress-nginx/ci/controller-service-internal-labels-values.yaml

Usage Example

controller:
  service:
    internal:
      enabled: true
      labels:
        external-dns.alpha.kubernetes.io/hostname: internal.example.com
        custom-label: test-value

Backward Compatibility
This change maintains backward compatibility by:

• Not changing behavior for existing configurations
• Only removing restrictions (required annotations)
• Preserving all existing label inheritance where appropriate
• Not requiring configuration of internal labels

Checklist

• [ ✅ ] Code follows repository style and conventions
• [ ✅ ] Templates render correctly
• [ ✅ ] Added test configuration
• [ ✅ ] Maintains backward compatibility
• [ ✅ ] Verified label isolation works as expected