Configuration apply error from applying 2 Prometheus plugins against 1 `Service` fails to be parsed about kubernetes-ingress-controller

[programmer04]

Currently, events are generated properly

• logs

  [ingress-controller] 2024-05-06T08:18:28Z        debug   Sending configuration to gateway clients        {"v": 1, "urls": ["https://10.244.0.8:8444", "https://10.244.0.9:8444"]}
  [ingress-controller] 2024-05-06T08:18:28Z        debug   events  failed to apply Kong configuration to https://10.244.0.9:8444: failed posting new config to /config: got status code 400        {"v": 1, "type": "Warning", "object": {"kind":"Pod","namespace":"kong","name":"ingress-kong-5cb656bbf8-g997d","apiVersion":"v1"}, "reason": "KongConfigurationApplyFailed"}
  [ingress-controller] 2024-05-06T08:18:28Z        debug   events  invalid plugin:prometheus: uniqueness violation: 'plugins' entity with primary key set to '4aeffa30-fd1b-5b9e-80d7-2dc1b0180f92' already declared       {"v": 1, "type": "Warning", "object": {"kind":"KongPlugin","namespace":"default","name":"prometheus-2","uid":"0d6617ff-8b4f-4d6e-844b-18fac946587f","apiVersion":"configuration.konghq.com/v1"}, "reason": "KongConfigurationApplyFailed"}
  [ingress-controller] 2024-05-06T08:18:28Z        debug   No configuration change, skipping sync to Kong  {"url": "https://10.244.0.8:8444", "v": 1}
  

• events

  ...
  default     2m59s       Warning   KongConfigurationApplyFailed   kongplugin/prometheus-1                   invalid plugin:prometheus: uniqueness violation: 'plugins' entity with primary key set to '4aeffa30-fd1b-5b9e-80d7-2dc1b0180f92' already declared
  default     3m59s       Warning   KongConfigurationApplyFailed   kongplugin/prometheus-2                   invalid plugin:prometheus: uniqueness violation: 'plugins' entity with primary key set to '4aeffa30-fd1b-5b9e-80d7-2dc1b0180f92' already declared
  ...
  kong        7m2s        Warning   KongConfigurationApplyFailed   pod/ingress-kong-5cb656bbf8-g997d         failed to apply Kong configuration to https://10.244.0.8:8444: failed posting new config to /config: got status code 400
  kong        2m2s        Warning   KongConfigurationApplyFailed   pod/ingress-kong-5cb656bbf8-g997d         failed to apply Kong configuration to https://10.244.0.9:8444: failed posting new config to /config: got status code 400
  ...
  

So the part of improving the validation webhook to reject such invalid configuration only left