Allow effects for addressable LEDs to work on "groups" of N LEDs instead of single LEDs

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

I have just made some "Smart Nano leaf replicas" like these https://www.thingiverse.com/thing:3354082 and put three WS2811 LEDs in each corner. The project on thingiverse comes with some firmware, but I obviously wanted to use esphome instead :)

It was easy to get things to light up with a configuration like below:

```
light:
- platform: fastled_clockless
chipset: WS2811
pin: D7
num_leds: 9
rgb_order: GRB
name: "FastLED WS2811 Light"
effects:
- addressable_random_twinkle:
name: Random Twinkle Effect With Custom Values
twinkle_probability: 5%
progress_interval: 32ms
```

My problem is that when I use things like the twinkle effect, it twinkle the single LEDs instead of each corner, since each corner is 3 LEDs and not just one.

It would be perfect if I could specify a "group_leds: 3" or similar to make the effects work on corners instead of single LEDs.

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

It would look way cooler ..

**Additional context**