UnicodeDecodeError: 'utf-8' codec can't decode byte 0xe7 in position 15: invalid continuation byte

Hello

When I try to send special character in metadata like "ç" I got this error.

The stack trace is:
```
Traceback (most recent call last):
File "src/python/grpcio/grpc/_cython/_cygrpc/grpc_string.pyx.pxi", line 48, in grpc._cython.cygrpc._decode
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xe7 in position 15: invalid continuation byte
```

I look a bit and tryed to encode my header value with encodeUri but even is the error disapear I need to decode in the backend.
I was wondering what was the best practices to avoid this error ?

PS: I use grpc-web@1.3.1