gRPC C++ compression interface support

[Andrew Liang]

Hi,

grpc-go support registers the compressor with gRPC by its name as following:

```

func RegisterCompressor(c Compressor) {
    registeredCompressor[c.Name()] = c
}

``` 

github link: https://github.com/grpc/grpc-go/blob/master/encoding/encoding.go

How to register my customize a compressor like grpc-go when using c++ ?

Thank you all.

[Lidi Zheng]

See https://groups.google.com/g/grpc-io/c/048jQeimZMo.

All available compression algorithm can be found at https://github.com/grpc/grpc/blob/master/include/grpc/impl/codegen/compression_types.h. Currently there is no way to customize compression algorithm for gRPC C++.