WLED: Fallback-Effect

**Describe the problem you have/What new integration you would like**

It would be nice, if the WLED effect could delegate to a specific effect while the LEDs are "blanked".

**Please describe your use case for this integration and alternatives you've tried:**

In my usecase I am building an RGB-Controller for controlling my PC's lighting according to system metrics ([rgbtop](https://github.com/klaernie/rgbtop)).
As power to the esphome device is controlled with the power supply, I don't really need a blank LED state, but rather would like it to use an effect so signify the "PC is on, but no data is being received" state.

**Additional context**