[DX] add RectorConfig::command() to ease external command registration (

#5443)

src/Config/RectorConfig.php

@@ -222,6 +222,15 @@ public function collector(string $collectorClass): void
         $this->tag($collectorClass, Collector::class);
     }
 
+    /**
+     * @param class-string<Command> $commandClass
+     */
+    public function command(string $commandClass): void
+    {
+        $this->singleton($commandClass);
+        $this->tag($commandClass, Command::class);
+    }
+
     public function import(string $filePath): void
     {
         if (str_contains($filePath, '*')) {