feat(ssh+cli): Support SSH CLI on machine init and add commands (#173)

* Add SSHCLIRemote type with buildSSHArgs

Implement's Executor interface (Run, Stream, Close)

* Add UseSSHCLI field to RemoteMachine struct

Allow us to differentiate regular ssh from ssh+cli.

* Parse ssh+cli:// scheme on machine init/add

* Support SSH CLI when provisioning

* Update docs to reflect ssh+cli:// support

* Revert removal of `init` examples

Fixes copy & pasta mistake when documenting the new ssh+cli connection
methods.

internal/sshexec/sshcli_test.go

@@ -0,0 +1,76 @@
+package sshexec
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestSSHCLIRemote_buildSSHArgs(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name     string
+		user     string
+		host     string
+		port     int
+		keyPath  string
+		expected []string
+	}{
+		{
+			name:     "default port, no key",
+			user:     "root",
+			host:     "example.com",
+			port:     22,
+			keyPath:  "",
+			expected: []string{"-o", "ConnectTimeout=5", "root@example.com"},
+		},
+		{
+			name:     "custom port",
+			user:     "ubuntu",
+			host:     "192.168.1.10",
+			port:     2222,
+			keyPath:  "",
+			expected: []string{"-o", "ConnectTimeout=5", "-p", "2222", "ubuntu@192.168.1.10"},
+		},
+		{
+			name:     "with key path",
+			user:     "root",
+			host:     "example.com",
+			port:     22,
+			keyPath:  "/path/to/key",
+			expected: []string{"-o", "ConnectTimeout=5", "-i", "/path/to/key", "root@example.com"},
+		},
+		{
+			name:     "all options",
+			user:     "admin",
+			host:     "server.local",
+			port:     2222,
+			keyPath:  "~/.ssh/id_rsa",
+			expected: []string{"-o", "ConnectTimeout=5", "-p", "2222", "-i", "~/.ssh/id_rsa", "admin@server.local"},
+		},
+		{
+			name:     "port zero (default)",
+			user:     "root",
+			host:     "example.com",
+			port:     0,
+			keyPath:  "",
+			expected: []string{"-o", "ConnectTimeout=5", "root@example.com"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			remote := &SSHCLIRemote{
+				user:    tt.user,
+				host:    tt.host,
+				port:    tt.port,
+				keyPath: tt.keyPath,
+			}
+			result := remote.buildSSHArgs()
+			assert.Equal(t, tt.expected, result)
+		})
+	}
+}