Cannot migrate a replica cluster externalCluster to the plugin

[fcanovai]

After changing from an externalCluster based on an in-tree barman-cloud to a plugin-based one, there are not enough permission to read the objectstore.

This doesn't happen when a cluster is created with a plugin-based externalCluster from the beginning.

[leonardoce]

This is the corresponding error message:

{"level":"info","ts":"2025-05-07T11:22:18.43281369Z","msg":"Patching role","name":"cluster-example","namespace":"default","name":"cluster-example-barman-cloud","namespace":"default","rules":[{"verbs":["get","watch","list"],"apiGroups":["barmancloud.cnpg.io"],"resources":["objectstores"],"resourceNames":["minio-store-bisonda"]},{"verbs":["update"],"apiGroups":["barmancloud.cnpg.io"],"resources":["objectstores/status"],"resourceNames":["minio-store-bisonda"]},{"verbs":["get","watch","list"],"apiGroups":[""],"resources":["secrets"],"resourceNames":["minio"]}]}
{"level":"info","ts":"2025-05-07T11:22:18.446879348Z","logger":"KubeAPIWarningLogger","msg":"unknown field \"metadata\""}
{"level":"info","ts":"2025-05-07T11:22:18.446955995Z","logger":"KubeAPIWarningLogger","msg":"unknown field \"rules\""}
{"level":"error","ts":"2025-05-07T11:22:18.447056608Z","msg":"Error while handling GRPC request","info":{"Server":{"Client":{}},"FullMethod":"/cnpgi.reconciler.v1.ReconcilerHooks/Pre"},"error":"the name of the object (cluster-example-barman-cloud based on URL) was undeterminable: name must be provided","stacktrace":"github.com/cloudnative-pg/machinery/pkg/log.(*logger).Error\n\t/go/pkg/mod/github.com/cloudnative-pg/machinery@v0.2.0/pkg/log/log.go:125\ngithub.com/cloudnative-pg/cnpg-i-machinery/pkg/pluginhelper/http.(*Server).Start.logFailedRequestsUnaryServerInterceptor.func2\n\t/go/pkg/mod/github.com/cloudnative-pg/cnpg-i-machinery@v0.3.0/pkg/pluginhelper/http/grpc.go:51\ngoogle.golang.org/grpc.NewServer.chainUnaryServerInterceptors.chainUnaryInterceptors.func1\n\t/go/pkg/mod/google.golang.org/grpc@v1.72.0/server.go:1208\ngithub.com/cloudnative-pg/cnpg-i/pkg/reconciler._ReconcilerHooks_Pre_Handler\n\t/go/pkg/mod/github.com/cloudnative-pg/cnpg-i@v0.2.1/pkg/reconciler/reconciler_grpc.pb.go:174\ngoogle.golang.org/grpc.(*Server).processUnaryRPC\n\t/go/pkg/mod/google.golang.org/grpc@v1.72.0/server.go:1405\ngoogle.golang.org/grpc.(*Server).handleStream\n\t/go/pkg/mod/google.golang.org/grpc@v1.72.0/server.go:1815\ngoogle.golang.org/grpc.(*Server).serveStreams.func2.1\n\t/go/pkg/mod/google.golang.org/grpc@v1.72.0/server.go:1035"}