admin: convert filer address to gRPC form before dispatch (#9523)

The master returns each registered filer in pb.ServerAddress dual-port
form (host:httpPort.grpcPort, e.g. 10.0.0.1:8888.18888). The admin's
plugin context builder forwarded that string verbatim as
filer_grpc_address, so workers calling grpc.DialContext on it failed
every job in ~3ms with "dial tcp: lookup tcp/8888.18888: unknown port".

Run each entry through pb.ServerAddress.ToGrpcAddress before populating
ClusterContext.FilerGrpcAddresses.

The lifecycle integration test now pins filer.port.grpc to a value that
breaks the FILER_PORT+10000 assumption, and a new dispatch test drives
the admin's /api/plugin/job-types/s3_lifecycle/run path end-to-end and
asserts the dispatched job both reaches the filer and deletes the
backdated object.

.github/workflows/s3-go-tests.yml

@@ -257,6 +257,7 @@ jobs:
         # TTL-pinned bucket collections piled up in a single run.
         test:
           - TestLifecycleAbortIncompleteMultipartUpload
+          - TestLifecycleAdminDispatchSucceedsWithCustomFilerGrpcPort
           - TestLifecycleBootstrapWalkOnExistingObjects
           - TestLifecycleConfigUpdateBetweenSweeps
           - TestLifecycleDeleteBucketLifecycleStopsDispatching