Introduce ClusterBundle API as a copy of Bundle

[erikgb]

Initial PR to implement #485 - when the design is approved.

/hold

[cert-manager-prow]

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[erikgb]

/test pull-trust-manager-smoke

[cert-manager-prow]

@erikgb: 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
pull-trust-manager-smoke	967474a	link	true	/test pull-trust-manager-smoke

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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