cleanup minio-cleanup-pre-upgrade and thanos-uninstall-pre-upgrade

In 1.1.1 release, thanos was configured to use minio-monitoring-tenant tenant (and single-replica-storageclass when longhorn was used). This tenant is replaced by minio-monitoring-tenant. As this value can't be updated, and thanos data will be lost in any case, uninstall is needed prior to upgrade cluster and reinstall it with new values. Also in 1.1.1 release, minio-monitoring-tenant was configured to use single-replica-storageclass, this tenant will be deleted during upgrade, but we have to delete the PVC that will be left over. Once release Sylva 1.2 these are no longer needed. Closes #1902 (closed)