Support generated code use package in right way without option go_package

[alx696]

Is your feature request related to a problem? Please describe.
Without option go_package, generated code lost import define, have different package name but placed in one directory.

Describe the solution you'd like
Auto generated code with package in right way.

Describe alternatives you've considered

1. Re-use import_path, define the base import path of import proto in generated code. Such as lilu.red/project_name, son.pb.go will import father from: lilu.red/project_name/auto/grpc/father
2. Generate folders like Java. package auto.grpc.father; will generated directory auto/grpc/father. Its better to distinguish the same name struct in different package.

Currently: option go_package need to be defined in every proto file, and not support batch generation #790 . package auto.grpc.son in generated code is package auto_grpc_son, lost import, and put then in same place(Golang not allow different package in one directory)!!

Additional context
father.proto

syntax = "proto3";

package auto.grpc.father;
//option go_package = "lilu.red/proto/auto/grpc/father";

message Info {
  string name = 1;
}

son.proto

syntax = "proto3";

package auto.grpc.son;
//option go_package = "lilu.red/proto/auto/grpc/son";

import "father.proto";

service SonService {
  rpc Insert (Info) returns (Info) {
  }
}

message Info {
  string id = 1; //auto set
  string name = 2;
  father.Info father = 3;
}

[dsnet]

We're moving towards a world where we double down on the presence of go_package. Any logic that tries to derive the Go package path from the information in protobuf alone leads to insanity in some way or another. The go_package option is the only way to have a sane understanding of how proto files relate to one another in the Go language.