[FLINK-36583] Add Slow Request Kube Client Metrics

[morhidi]

What is the purpose of the change

Adding a simple counter to monitor slow API requests, identifying those that exceed a predefined time threshold, e.g.:

kubernetes.client.metrics.slow.request.threshold=5s

Verifying this change

• Unit tests where added
• Manually can be verified by reducing the threshold to a very low number, e.g.:

kubernetes.client.metrics.slow.request.threshold=1 MILLISECOND

-- Counters ---------------------------------------------------------------------
flink-kubernetes-operator-b48954fcf-w8p4z.k8soperator.default.flink-kubernetes-operator.system.KubeClient.HttpRequest.Slow.Count: 87

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? yes
• If yes, how is the feature documented? docs added for the new propery

[morhidi]

cc @mxm @gyfora

[mxm]

Generally LGTM. A minor comment inline.

[mxm]

Based on what the test does, this name seems more appropriate:

Suggested change

	void shouldNotTrackResponseAsSlowResponseAboveThreshold() {
	void shouldTrackResponseAsSlowResponseAboveThreshold() {

[morhidi]

Correct, fixing