fix: 🐛 prevent reflection headers to be stored on the server

[petragabriela]

Similar to #42 but fixes the server reflection step. One user's metadata that is used as reflection headers could affect the next user's reflection headers.

STR:

1. Open grpcox on a browser tab and include some metadata when connecting to a grpc server
2. Open grpcox on a new browser tab and connect to a grpc server without any metadata
3. The MD previously used in Step 1 will be sent on the second request (Step 2) too

Fixes the bug by sending the reflection headers directly during server reflection instead of storing them on the Resource