[release-1.9] 🐛 Export runtime.Client interface and cache package

[k8s-infra-cherrypick-robot]

This is an automated cherry-pick of #11611

/assign sbueringer

[sbueringer]

/lgtm
/approve

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 5c9842552b3b7313dd61cb9211ad275d7195e4d4

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: sbueringer

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[k8s-ci-robot]

@k8s-infra-cherrypick-robot: 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-cluster-api-apidiff-release-1-9	9898cc6	link	false	/test pull-cluster-api-apidiff-release-1-9

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