add mutex lock to update managedclusterlist

[coleenquadros]

/test sonarcloud

[sonarcloud[bot]]

Quality Gate failed

Failed conditions
C Maintainability Rating on New Code (required ≥ A)

See analysis details on SonarCloud

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[coleenquadros]

/test test-e2e

[openshift-ci[bot]]

@coleenquadros: 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
ci/prow/sonarcloud	4ef83c51080284da12e10c263e1037690296f8ba	link	false	/test sonarcloud

Full PR test history. Your PR dashboard.

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[coleenquadros]

/test test-e2e

[openshift-ci[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: coleenquadros, subbarao-meduri

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/stolostron/multicluster-observability-operator/blob/main/OWNERS)~~ [coleenquadros,subbarao-meduri] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment