Deprecate white_value support in MQTT light

[emontnemery]

Breaking change

Support for white_value is deprecated in MQTT light, and will be removed in Home Assistant Core 2022.9.
For MQTT light basic schema, white_value support is replaced by configuring support for white + either of hs, rgb, xy, or rgbw or rgbww.
For MQTT light JSON schema, white_value support is replaced by configuring support for color mode white + either of color modes hs, rgb, xy, or color mode rgbworrgbww`.

Proposed change

Deprecate white_value support in MQTT light

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

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