fix: resolve gRPC DNS resolution issues in Kubernetes #8384 (#8387)

* fix: resolve gRPC DNS resolution issues in Kubernetes #8384

- Replace direct `grpc.NewClient` calls with `pb.GrpcDial` for consistent connection establishment
- Fix async DNS resolution behavior in K8s with `ndots:5`
- Ensure high-level components use established helper for reliable networking

* refactor: refine gRPC DNS fix and add documentation

- Use instance's grpcDialOption in BrokerClient.ConfigureTopic
- Add detailed comments to GrpcDial explaining Kubernetes DNS resolution rationale

* fix: ensure proper context propagation in broker_client gRPC calls

- Pass the provided `ctx` to `pb.GrpcDial` in `ConfigureTopic` and `GetUnflushedMessages`
- Ensures that timeouts and cancellations are correctly honored during connection establishment

* docs: refine gRPC resolver documentation and cleanup dead code

- Enhanced documentation for `GrpcDial` with explicit warnings about global state mutation when using `resolver.SetDefaultScheme("passthrough")`.
- Recommended `passthrough:///` prefix as the primary migration path for `grpc.NewClient`.
- Removed dead commented-out code for `grpc.WithBlock()` and `grpc.WithTimeout()`.

weed/filer_client/filer_discovery.go

@@ -51,7 +51,7 @@ func (fds *FilerDiscoveryService) discoverFilersFromMaster(masterAddr pb.ServerA
 	// Convert HTTP master address to gRPC address (HTTP port + 10000)
 	grpcAddr := masterAddr.ToGrpcAddress()
 
-	conn, err := grpc.NewClient(grpcAddr, fds.grpcDialOption)
+	conn, err := pb.GrpcDial(context.Background(), grpcAddr, false, fds.grpcDialOption)
 	if err != nil {
 		return nil, fmt.Errorf("failed to connect to master at %s: %v", grpcAddr, err)
 	}