[3.x] Separate services by namespace

[rez1dent3]

Now it is impossible to create two identical services with different packages. We need to try to solve this problem.

proto1.proto

syntax = "proto3";
package com.bavix.helloworld1;
service Greeter {
    rpc SayHello (HelloRequest) returns (HelloReply) {}
}

proto2.proto

syntax = "proto3";
package com.bavix.helloworld2;
service Greeter {
    rpc SayHello (HelloRequest) returns (HelloReply) {}
}

Introduce a mode that will make a safe transition from short service names to long ones. It might be worth adding depreacted to the logs.

[Tom-Hudson]

Need this. Would be awesome to have!