feat: try each cluster connection in order until one succeeds, add progress spinner

internal/cli/config/connection.go

@@ -1,6 +1,7 @@
 package config
 
 import (
+	"fmt"
 	"net"
 	"net/netip"
 	"strconv"
@@ -24,6 +25,15 @@ type MachineConnection struct {
 	PublicKey secret.Secret   `yaml:"public_key,omitempty"`
 }
 
+func (c MachineConnection) String() string {
+	if c.SSH != "" {
+		return string(c.SSH)
+	} else if c.TCP != nil && c.TCP.IsValid() {
+		return fmt.Sprintf("tcp://%s", c.TCP)
+	}
+	return "unknown connection"
+}
+
 // SSHDestination represents an SSH destination string in the canonical form of "user@host:port".
 // The default user "root" and port 22 can be omitted.
 type SSHDestination string