TUN-9469: Centralize UDP origin proxy dialing as ingress service

Introduces a new `UDPOriginProxy` interface and `UDPOriginService`
to standardize how UDP connections are dialed to origins. Allows for
future overrides of the ingress service for specific dial destinations.

Simplifies dependency injection for UDP dialing throughout both datagram
v2 and v3 by using the same ingress service. Previous invocations called
into a DialUDP function in the ingress package that was a light
wrapper over `net.DialUDP`. Now a reference is passed into both datagram
controllers that allows more control over the DialUDP method.

Closes TUN-9469

supervisor/supervisor.go

@@ -78,11 +78,14 @@ func NewSupervisor(config *TunnelConfig, orchestrator *orchestration.Orchestrato
 	edgeBindAddr := config.EdgeBindAddr
 
 	datagramMetrics := v3.NewMetrics(prometheus.DefaultRegisterer)
-	sessionManager := v3.NewSessionManager(datagramMetrics, config.Log, ingress.DialUDPAddrPort, orchestrator.GetFlowLimiter())
+	// No reserved ingress services for now, hence the nil
+	ingressUDPService := ingress.NewUDPOriginService(nil, config.Log)
+	sessionManager := v3.NewSessionManager(datagramMetrics, config.Log, ingressUDPService, orchestrator.GetFlowLimiter())
 
 	edgeTunnelServer := EdgeTunnelServer{
 		config:            config,
 		orchestrator:      orchestrator,
+		ingressUDPProxy:   ingressUDPService,
 		sessionManager:    sessionManager,
 		datagramMetrics:   datagramMetrics,
 		edgeAddrs:         edgeIPs,

supervisor/tunnel.go

@@ -166,6 +166,7 @@ func (f *ipAddrFallback) ShouldGetNewAddress(connIndex uint8, err error) (needsN
 type EdgeTunnelServer struct {
 	config            *TunnelConfig
 	orchestrator      *orchestration.Orchestrator
+	ingressUDPProxy   ingress.UDPOriginProxy
 	sessionManager    v3.SessionManager
 	datagramMetrics   v3.Metrics
 	edgeAddrHandler   EdgeAddrHandler
@@ -613,6 +614,7 @@ func (e *EdgeTunnelServer) serveQUIC(
 		datagramSessionManager = connection.NewDatagramV2Connection(
 			ctx,
 			conn,
+			e.ingressUDPProxy,
 			e.config.ICMPRouterServer,
 			connIndex,
 			e.config.RPCTimeout,