feat: omitempty Swarm.EnableRelayHop for circuit v1 migration (#157)

* re-add the Swarm.EnableRelayHop option
* make Swarm.EnableRelayHop omitempty

Co-authored-by: Marcin Rataj <lidel@lidel.org>

swarm.go

@@ -19,6 +19,12 @@ type SwarmConfig struct {
 	// `Swarm.Transports.Relay` if specified.
 	DisableRelay bool `json:",omitempty"`
 
+	// EnableRelayHop makes this node act as a public relay v1
+	//
+	// Deprecated: The circuit v1 protocol is deprecated.
+	// Use `Swarm.RelayService` to configure the circuit v2 relay.
+	EnableRelayHop bool `json:",omitempty"`
+
 	// EnableAutoRelay enables the "auto relay user" feature.
 	// Node will find and use advertised public relays when it determines that
 	// it's not reachable from the public internet.