Add light.brightness condition

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

I would like to request a light.brightness condition.

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

I'm coding dimmer logic and I want to stop dimming just before the light turns off (because the toggle is for that 😄).

**Additional context**

Example code:
```
- while:
condition:
- binary_sensor.is_on: switchID_1
- light.brightness:
id: dimmerID_1
above: 1
then:
- light.dim_relative:
id: dimmerID_1
relative_brightness: -1%
transition_length: 0.01s
- delay: 0.01s
```

Long example:
```
binary_sensor:
- platform: gpio
name: 'Switch 1'
id: switchID_1
pin:
number: GPIO14
mode: INPUT
internal: true
filters:
- delayed_on_off: 50ms
on_multi_click:

# single click
- timing:
- ON for at most 1s
- OFF for at least 0.5s
then:
- logger.log: "Single-Clicked"
- light.toggle: dimmerID_1

# Press and Hold button
- timing:
- ON for at most 0.5s
- OFF for at least 0.1s
- ON for at least 1s
then:
- logger.log: "Press and Hold - Dim DOWN"
- while:
condition:
- binary_sensor.is_on: switchID_1
- light.brightness:
id: dimmerID_1
above: 1
then:
- light.dim_relative:
id: dimmerID_1
relative_brightness: -1%
transition_length: 0.01s
- delay: 0.01s

# Hold button
- timing:
- ON for at least 1s
then:
- logger.log: "Hold - Dim UP"
- while:
condition:
- binary_sensor.is_on: switchID_1
then:
- light.dim_relative:
id: dimmerID_1
relative_brightness: +1%
transition_length: 0.01s
- delay: 0.01s

```

No source files, tests, or entry points are named. Start by locating the light condition implementations and the existing light state or brightness APIs; done means a light.brightness condition supports the shown threshold syntax for dimming logic.

Written by the indexing model from the issue text.