[8.17](backport #6360) [k8s] add kubernetes hints integration tests

[mergify]

What does this PR do?

This is the last part (I promise) of the PR series to add support for Kubernetes hints and integration tests for Redis. It introduces:

• Additional test cases to validate agent Kubernetes hints functionality using Redis as the hints-enabled workload:
  • When hints-enabled workloads pre-exist the agent deployment.
  • When hints-enabled workloads are deployed after the agent is already running.

Why is it important?

This PR completes the Kubernetes hints-based testing and it ensures that that Kubernetes hints functionality is thoroughly tested.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective or that my feature works
• I have added an integration test or an E2E test

Disruptive User Impact

There is no expected disruption for users as this PR only extends k8s integration tests.

How to test this PR locally

mage integration:auth
PLATFORMS=linux/arm64 EXTERNAL=true SNAPSHOT=true PACKAGES=docker mage -v package 
INSTANCE_PROVISIONER=kind STACK_PROVISIONER=stateful K8S_VERSION=v1.31.1 SNAPSHOT=true mage integration:kubernetes

Related issues

• Closes Include hints autodiscovery configuration inside integration tests for k8s #5660

---

This is an automatic backport of pull request #6360 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of c7c5ba4 has failed:

On branch mergify/bp/8.17/pr-6360
Your branch is up to date with 'origin/8.17'.

You are currently cherry-picking commit c7c5ba413.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	new file:   testing/integration/testdata/k8s.hints.redis.yaml

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   testing/integration/kubernetes_agent_standalone_test.go

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[pkoutsovasilis]

requires this PR to be merged first

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarQube