feat: add global labels to KongClusterPlugin

[battlebyte]

This change adds the global label to KongClusterPlugin in kong2kic to ensure proper transfer of semantics between deck declarative format and Ingress/Gateway API. Integration tests updated for Gateway resources.

Before this change:

apiVersion: configuration.konghq.com/v1
config:
  bandwidth_metrics: true
  latency_metrics: true
  per_consumer: true
  status_code_metrics: true
  upstream_health_metrics: true
kind: KongClusterPlugin
metadata:
  annotations:
    konghq.com/tags: cloudops-managed,metrics
    kubernetes.io/ingress.class: kong
  name: prometheus
plugin: prometheus

After this change:

apiVersion: configuration.konghq.com/v1
config:
  bandwidth_metrics: true
  latency_metrics: true
  per_consumer: true
  status_code_metrics: true
  upstream_health_metrics: true
kind: KongClusterPlugin
metadata:
  annotations:
    konghq.com/tags: cloudops-managed,metrics
    kubernetes.io/ingress.class: kong
  labels:
    global: "true"
  name: prometheus
plugin: prometheus

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 32.80%. Comparing base (b46c2fd) to head (1eb44f4).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1833      +/-   ##
==========================================
+ Coverage   32.79%   32.80%   +0.01%     
==========================================
  Files          73       73              
  Lines        6556     6557       +1     
==========================================
+ Hits         2150     2151       +1     
  Misses       4242     4242              
  Partials      164      164              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.