[FLINK-36599] Correct the metric config name in the doc to reduce confusing

[alnzng]

What is the purpose of the change

This PR is for fixing the name of the metric config which enables the response codes group in "Metrics and Logging" doc, to make the naming be consistent with information in "Configuration" doc.

Brief change log

• Add operator config prefix kubernetes.operator. to make it show the full name of the config

Verifying this change

This change is a trivial rework / code cleanup without any test coverage.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (no)
• The public API, i.e., is any changes to the CustomResourceDescriptors: (no)
• Core observer or reconciler logic that is regularly executed: (no)

Documentation

• Does this pull request introduce a new feature? (no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

[alnzng]

@gyfora A minor improvement for doc, would you mind helping take a look?