MON-4398: Enable UTF-8 by default in admission-webhook

[slashpai]

Ref: prometheus-operator v0.86.0 introduced the new flag to admission webhook to choose between validation scheme.
https://github.com/prometheus-operator/prometheus-operator/blob/cc19d0e3fc10ba4e7f325d7e30bc80677a55b5fb/cmd/admission-webhook/main.go#L55

• I added CHANGELOG entry for this change.
• No user facing changes, so no entry in CHANGELOG was needed.

[openshift-ci-robot]

@slashpai: This pull request references MON-4398 which is a valid jira issue.

Warning: The referenced jira issue has an invalid target version for the target branch this PR targets: expected the story to target the "4.21.0" version, but no target version was set.

In response to this:

Ref: prometheus-operator v0.86.0 introduced the new flag to admission webhook to choose between validation scheme.
https://github.com/prometheus-operator/prometheus-operator/blob/cc19d0e3fc10ba4e7f325d7e30bc80677a55b5fb/cmd/admission-webhook/main.go#L55

• I added CHANGELOG entry for this change.
• No user facing changes, so no entry in CHANGELOG was needed.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the openshift-eng/jira-lifecycle-plugin repository.

[slashpai]

/skip

[slashpai]

/retest-required

[slashpai]

@simonpasquier I removed amcfg test should be good now

[simonpasquier]

/lgtm

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: simonpasquier, slashpai

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[slashpai]

/retest-required

[simonpasquier]

/skip

[simonpasquier]

/test e2e-hypershift-conformance

[juzhao]

/retest-required

[openshift-ci]

@slashpai: The following tests 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/ginkgo-tests	4add0cf	link	false	/test ginkgo-tests
ci/prow/versions	4add0cf	link	false	/test versions
ci/prow/okd-scos-e2e-aws-ovn	4add0cf	link	false	/test okd-scos-e2e-aws-ovn
ci/prow/e2e-hypershift-conformance	4add0cf	link	true	/test e2e-hypershift-conformance

Full PR test history. Your PR dashboard.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository. I understand the commands that are listed here.