Migrate away from deprecated ioutil

[sebrandon1]

ioutil has been deprecated since Go 1.16: https://go.dev/doc/go1.16#ioutil

Tracking issue: redhat-best-practices-for-k8s/telco-bot#52

Migration from ioutil to os/io functions:

• Replaced ioutil.TempFile with os.CreateTemp in generateTempCertificates() in pkg/metrics/server_test.go. [1] [2]
• Replaced ioutil.ReadFile with os.ReadFile in GetNamespace() in pkg/stub/handler.go, and in file reading methods in pkg/stub/interfaces.go. [1] [2] [3]
• Replaced ioutil.ReadDir with os.ReadDir and updated logic to convert DirEntry to FileInfo in DefaultResourceFileLister.List() in pkg/stub/interfaces.go.
• Replaced ioutil.ReadAll with io.ReadAll in dumpPod() in test/e2e/cluster_samples_operator_test.go.

Imports cleanup:

• Removed unused ioutil imports and added io where needed in affected files. [1] [2] [3] [4]

[openshift-ci]

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[openshift-ci]

@sebrandon1: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/okd-scos-images	6b04c9b	link	true	/test okd-scos-images

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