Rename 'permanent_slots' field to 'slots'

docs/reference/cluster_manifest.md

manifests/complete-postgres-manifest.yaml

pkg/apis/acid.zalan.do/v1/postgresql_type.go

pkg/apis/acid.zalan.do/v1/util_test.go

pkg/apis/acid.zalan.do/v1/zz_generated.deepcopy.go

pkg/cluster/k8sres.go