Terminal informer after tenant cluster removed

[vincent-pli]

What this PR does / why we need it:

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 #162

[k8s-ci-robot]

Hi @vincent-pli. Thanks for your PR.

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[gyliu513]

/ok-to-test

[Fei-Guo]

/approve /lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Fei-Guo, vincent-pli

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Needs approval from an approver in each of these files: - ~~[virtualcluster/OWNERS](https://github.com/kubernetes-sigs/cluster-api-provider-nested/blob/main/virtualcluster/OWNERS)~~ [Fei-Guo] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment