Migrate the openshift/router repository away from the deprecated ioutil package.

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

Changes include:

• Replace ioutil.ReadFile/WriteFile with os.ReadFile/os.WriteFile
• Replace ioutil.TempFile/TempDir with os.CreateTemp/os.MkdirTemp
• Replace ioutil.NopCloser/Discard with io.NopCloser/io.Discard
• Remove all ioutil imports

PR: https://github.com/openshift/router/pull/693
Tracking issue: https://github.com/redhat-best-practices-for-k8s/telco-bot/issues/52