[release-1.8] 🐛 Export runtime.Client interface and cache package

[sbueringer]

Signed-off-by: Stefan Büringer [email protected]

What this PR does / why we need it:
Manual cherry-pick of #11611

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

[k8s-ci-robot]

@sbueringer: 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-1-8	24c449f	link	false	/test pull-cluster-api-apidiff-release-1-8

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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[chrischdi]

/lgtm
/approve

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 3aa2f0bb8d0ca863fbbd60e8d160a59806cb4647

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: chrischdi

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