Add introduction of raw error dump endpoint in KIC diagnostics server

[randmonkey]

Where is the problem?

https://docs.konghq.com/kubernetes-ingress-controller/latest/reference/troubleshooting/

What happened?

KIC 3.2 added an endpoint to dump the raw error message from Kong gateway when failed to apply configuration. We need to introduce the usage of the endpoint.

What did you expect to happen?

The troubleshooting page should contain a section to introduce the raw error dumping endpoint.

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