[SPARK-39701][CORE][K8S][TESTS] Move withSecretFile to SparkFunSuite to reuse

[dongjoon-hyun]

What changes were proposed in this pull request?

This PR aims to move withSecretFile to SparkFunSuite and reuse it in Kubernetes tests.

Why are the changes needed?

Currently, K8s unit tests generate a leftover because it doesn't clean up the temporary secret files. By reusing the existing method, we can avoid this

$ build/sbt -Pkubernetes "kubernetes/test"
$ git status
On branch master
Your branch is up to date with 'apache/master'.

Untracked files:
  (use "git add <file>..." to include in what will be committed)
	resource-managers/kubernetes/core/temp-secret/

Does this PR introduce any user-facing change?

No. This is a test-only change.

How was this patch tested?

Pass the CIs.

[dongjoon-hyun]

Could you review this, @viirya ?

[viirya]

lgtm

[dongjoon-hyun]

Thank you, @viirya . Merged to master.