Flux breaks on upgrade from 1.3 if Thanos is disabled

In Sylva 1.3 the single-replica-storageclass unit which creates this storageClass has an enabled condition on minio-monitoring being enabled which itself is conditioned on Thanos. In Sylva 1.4 and newer Flux source controller is set to use this storageClass and since Flux is the first unit upgraded it will fail if the storageClass is not present (if monitoring or thanos were previously disabled), blocking the advancement of the upgrade.

We need, in case of upgrade, to remove the dependencies of the single-replica-storageclass and have flux depend on it.

cc: @tmmorin