fix(migrations): add instructions to bring back custom_migration_cutoff #9662

Job	Run time
execution-plan / execution_plan	40s
execution-plan / ${{ matrix.data.directory }} - Build and Publish	0s
execution-plan / services/frontend-service - Build and Publish	6m 20s
execution-plan / services/manifest-repo-export-service - Build and Publish	3m 29s
execution-plan / services/cd-service - Build and Publish	5m 21s
execution-plan / services/cloudrun-service - Build and Publish	3m 28s
execution-plan / services/rollout-service - Build and Publish	6m 23s
execution-plan / Cleanup	0s
integration-tests / integration-test	5m 13s
trivy-scan / trivy	1m 6s
	32m 0s

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