chore: generate a minimal Caddyfile with verify handler alongside caddy.json

internal/machine/caddyconfig/caddyfile.go

@@ -0,0 +1,17 @@
+package caddyconfig
+
+import (
+	"fmt"
+
+	"github.com/psviderski/uncloud/pkg/api"
+)
+
+func GenerateCaddyfile(containers []api.ServiceContainer, verifyResponse string) (string, error) {
+	return fmt.Sprintf(`http:// {
+	handle %s {
+		respond "%s" 200
+	}
+	log
+}
+`, VerifyPath, verifyResponse), nil
+}