add Subscription management apis to service

[rysweet]

What feature would you like to be added?

need to add support for
message TypeSubscription {
string topic_type = 1;
string agent_type = 2;
}

message Subscription {
oneof subscription {
TypeSubscription typeSubscription = 1;
}
}

message AddSubscriptionRequest {
string request_id = 1;
Subscription subscription = 2;
}

message AddSubscriptionResponse {
string request_id = 1;
bool success = 2;
optional string error = 3;
}

Why is this needed?

xlang combat