Make simple initial test case

This commit makes the initial SSH test a bit simpler:

- Use the same pattern/functions for all clients as other tests
- Only test within _one_ namespace/user to confirm the base case
- Use retry function, same as taildrop, there is some funky going on
  there...

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

integration/tsic/tsic.go

@@ -47,6 +47,7 @@ type TailscaleInContainer struct {
 	// optional config
 	headscaleCert     []byte
 	headscaleHostname string
+	withSSH           bool
 }
 
 type Option = func(c *TailscaleInContainer)
@@ -83,6 +84,12 @@ func WithHeadscaleName(hsName string) Option {
 	}
 }
 
+func WithSSH() Option {
+	return func(tsic *TailscaleInContainer) {
+		tsic.withSSH = true
+	}
+}
+
 func New(
 	pool *dockertest.Pool,
 	version string,
@@ -219,6 +226,10 @@ func (t *TailscaleInContainer) Up(
 		t.hostname,
 	}
 
+	if t.withSSH {
+		command = append(command, "--ssh")
+	}
+
 	if _, _, err := t.Execute(command); err != nil {
 		return fmt.Errorf("failed to join tailscale client: %w", err)
 	}