update docs about helm and cluster configuration

charts/postgres-operator/values.yaml

docker/logical-backup/Dockerfile

docker/logical-backup/dump.sh

docs/administrator.md

docs/developer.md

docs/quickstart.md

docs/reference/cluster_manifest.md

docs/reference/operator_parameters.md

docs/user.md

manifests/complete-postgres-manifest.yaml

manifests/configmap.yaml

manifests/postgresql-operator-default-configuration.yaml

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

pkg/cluster/database.go

pkg/controller/operator_config.go

pkg/util/config/config.go