Import shelly in the executor to avoid blocking the event loop (#111623)

`[homeassistant.loader] Component shelly import took 0.396 seconds (loaded_executor=False)`

homeassistant/components/shelly/manifest.json

@@ -5,6 +5,7 @@
   "config_flow": true,
   "dependencies": ["bluetooth", "http"],
   "documentation": "https://www.home-assistant.io/integrations/shelly",
+  "import_executor": true,
   "integration_type": "device",
   "iot_class": "local_push",
   "loggers": ["aioshelly"],