bump to v1.8.1 (#1884)

.github/ISSUE_TEMPLATE/postgres-operator-issue-template.md

charts/postgres-operator-ui/Chart.yaml

charts/postgres-operator-ui/index.yaml

charts/postgres-operator-ui/postgres-operator-ui-1.8.1.tgz

charts/postgres-operator-ui/values.yaml

charts/postgres-operator/Chart.yaml

charts/postgres-operator/crds/operatorconfigurations.yaml

charts/postgres-operator/index.yaml

charts/postgres-operator/postgres-operator-1.8.1.tgz

charts/postgres-operator/values.yaml

docs/administrator.md

docs/reference/operator_parameters.md

kubectl-pg/go.mod

manifests/configmap.yaml

manifests/operatorconfiguration.crd.yaml

manifests/postgres-operator.yaml

manifests/postgresql-operator-default-configuration.yaml

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

pkg/controller/operator_config.go

pkg/util/config/config.go