Add color_mode support to MQTT JSON light

[emontnemery]

Breaking change

MQTT JSON light now supports color_mode which should be used together with supported_color_modes to signal the light's features.
Feature flags color_temp, hs, rgb, white_value, xy are all deprecated and support will be removed in 2021.10.

Proposed change

Add color_mode support to MQTT JSON light.

color_mode will not be sent to the light on the command topic, the light can unambiguously deduce the desired color made based on which values are present in the color dict or if color_temp is present.

The light must report a supported color_mode in it's state update if the state update includes a color dict or if color_temp is present.

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

Example entry for configuration.yaml:

# Example configuration.yaml
light:
  - platform: "mqtt"
    schema: "json"
    "brightness": True,
    "color_mode": True,
    "command_topic": "test_light/set",
    "name": "test",
    "platform": "mqtt",
    "supported_color_modes": ["color_temp", "hs"]

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
• Link to documentation pull request: Add color_mode support to MQTT JSON light home-assistant.io#17205

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
• The code has been formatted using Black (black --fast homeassistant tests)
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io

If the code communicates with devices, web services, or third-party tools:

• The manifest file has all fields filled out correctly.
  Updated and included derived files by running: python3 -m script.hassfest.
• New or updated dependencies have been added to requirements_all.txt.
  Updated by running python3 -m script.gen_requirements_all.
• Untested files have been added to .coveragerc.

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[emontnemery]

@Koenkk Can you please help to review this change?

[Koenkk]

Looks good, no comments from my side.

[emontnemery]

@Koenkk Are you OK with the non-symmetric way color_mode will be used in commands and state updates?

For example, the light will get this command:

{"state": "ON", "color": {"h": 359.0, "s": 78.0}, "brightness": 75}

To which the expected state update from the light is:

{"state": "ON", "color_mode": "hs", "color": {"h": 359.0, "s": 78.0}, "brightness": 75}

This means the light may include some additional data, such as color_temp when it's in hs state, which will be ignored by Home Assistant.

[Koenkk]

@emontnemery yes!

[frenck]

This looks really great!

Only docs are missing