public GrpcClientBuilder pathPrefix(String prefix) {
        requireNonNull(prefix, "prefix");
        checkArgument(!prefix.isEmpty(), "prefix is empty.");
        checkArgument(prefix.charAt(0) == '/', "prefix: %s (must start with '/')", prefix);

        if (!prefix.endsWith("/")) {
            prefix += '/';
        }
        this.prefix = prefix;
        return this;
    }
Sets the context path for the gRPC endpoint.
This method will be useful if your gRPC service is bound to a context path.
For example:
<pre>{@code
// A gRPC service is bound to "/grpc/com.example.MyGrpcService/"
Server.builder()
      .serviceUnder("/grpc", GrpcService.builder()
                                        .addService(new MyGrpcService())
                                        .build())
      .build();

// Prefix "/grpc" to the gRPC service path.
GrpcClient.builder("https://api.example.com")
          .pathPrefix("/grpc")
          .build(MyGrpcServiceGrpc.XXXStub.class)
}</pre>
grpc/src/main/java/com/linecorp/armeria/client/grpc/GrpcClientBuilder.java