Additional headers -H works with grpcurl but not grpcui

Is there some difference between how headers are passed in grpcui compared to grpcurl?

Using grpcurl:
```
% grpcurl -plaintext -H "my-token:$MY_TOKEN" :30080 list
gateway.Gateway
grpc.reflection.v1alpha.ServerReflection
```

Using grpcui:
```
% grpcui -plaintext -H "my-token:$MY_TOKEN" :30080
Failed to compute set of methods to expose: rpc error: code = Unauthenticated desc = No auth token present
```

Start by comparing how grpcui and grpcurl process the shown -H header during service reflection. Reproduce the grpcui command and verify that the header is included in the reflection request so the command can list methods without the unauthenticated error.

Written by the indexing model from the issue text.