CustomDNS feature enablement along with inclusion of 4.21 upstream installer

[shaheen0b111]

Initial changes includes

• 4.21 upstream installer changes
• CustomDNS feature flag set

[openshift-ci]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: shaheen0b111
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[openshift-ci]

@shaheen0b111: 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/validate	363e6d5	link	true	/test validate
ci/prow/lint	363e6d5	link	true	/test lint
ci/prow/unit	363e6d5	link	true	/test unit
ci/prow/vendor	363e6d5	link	true	/test vendor

Full PR test history. Your PR dashboard.

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