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:

• Replaced ioutil.TempFile with os.CreateTemp in integration.go for creating temporary kubeconfig files.
• Replaced ioutil.TempDir with os.MkdirTemp in testserver.go for creating temporary directories.
• Updated imports in integration.go, testserver.go, and tokenreviews.go to remove ioutil and add os or io as needed. [1] [2] [3]
• Replaced ioutil.ReadAll with io.ReadAll in tokenreviews.go for reading HTTP response bodies. [1] [2]

[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/e2e-aws-upgrade	d35f3ed	link	true	/test e2e-aws-upgrade

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