[release-4.18]: add OnClusterBuilds to default config

[cheesesashimi]

This effectively makes OnClusterBuild no longer require TechPreviewNoUpgrade to be enabled before making use of this feature in 4.18.z. Similar work has already landed in 4.19.

[openshift-ci]

Hello @cheesesashimi! Some important instructions when contributing to openshift/api:
API design plays an important part in the user experience of OpenShift and as such API PRs are subject to a high level of scrutiny to ensure they follow our best practices. If you haven't already done so, please review the OpenShift API Conventions and ensure that your proposed changes are compliant. Following these conventions will help expedite the api review process for your PR.

[openshift-ci]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[openshift-ci]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: cheesesashimi
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[sergiordlr]

Verified using IPI on AWS

All MCO e2e OCB test cases pased

[cheesesashimi]

/test e2e-gcp

[openshift-ci]

@cheesesashimi: 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/verify-crd-schema	34bde19	link	true	/test verify-crd-schema
ci/prow/okd-scos-e2e-aws-ovn	34bde19	link	false	/test okd-scos-e2e-aws-ovn
ci/prow/verify	34bde19	link	true	/test verify
ci/prow/e2e-gcp	34bde19	link	false	/test e2e-gcp

Full PR test history. Your PR dashboard.

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