Proposal to have the DiscoveryService to do bidirectional sync

Currently, the DiscoveryService allows only unidirectional sync. One of the challenges with this approach is that most agents implementing this interface need to be publicly available.

hamlet/api/resourcediscovery/v1alpha1/resource_discovery.proto

Lines 88 to 95 in 9a69c19

    
           // DiscoveryService represents the API implemented by a federated service mesh 
        
           // owner. 
        
           service DiscoveryService { 
        
             // Establish a new stream with a federated service mesh owner. The federated 
        
             // service mesh owner can then send StreamResponse messages, and the federated 
        
             // service mesh consumer can ACK/NACK these via new StreamRequest messages. 
        
             rpc EstablishStream (stream StreamRequest) returns (stream StreamResponse); 
        
           }

The proposal is to change the interface in a way that service discovery works seamlessly even when only one of the agents is publicly available while the rest may not.

-  rpc EstablishStream (stream StreamRequest) returns (stream StreamResponse);
+  rpc EstablishPublishStream (stream StreamRequest) returns (stream StreamResponse);
+  rpc EstablishSubscribeStream (stream StreamResponse) returns (stream StreamRequest);

/cc @sergiopozoh

Pending #25

	// DiscoveryService represents the API implemented by a federated service mesh
	// owner.
	service DiscoveryService {
	// Establish a new stream with a federated service mesh owner. The federated
	// service mesh owner can then send StreamResponse messages, and the federated
	// service mesh consumer can ACK/NACK these via new StreamRequest messages.
	rpc EstablishStream (stream StreamRequest) returns (stream StreamResponse);
	}