chore(client/v3/naming): deprecate Metadata field in Endpoint struct

resolves: #19706

Signed-off-by: amosehiguese <[email protected]>

Author: amosehiguese

client/v3/naming/endpoints/endpoints.go

@@ -18,7 +18,9 @@ type Endpoint struct {
 	// Metadata is the information associated with Addr, which may be used
 	// to make load balancing decision.
 	// Since etcd 3.1
-	Metadata interface{}
+	//
+	// Deprecated: The field is deprecated and will be removed in 3.7.
+	Metadata any
 }
 
 type Operation uint8