Allow specifying an icon for a scene

[balloob]

Breaking change

Proposed change

Add a new icon configuration parameter to specify an icon for a scene.

Also realized ID was missing from config validation, added it.

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

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
• Link to documentation pull request:

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.

The integration reached or maintains the following Integration Quality Scale:

• No score or internal
• 🥈 Silver
• 🥇 Gold
• 🏆 Platinum

[probot-home-assistant]

Hey there @home-assistant/core, mind taking a look at this pull request as its been labeled with a integration (homeassistant) you are listed as a codeowner for? Thanks!

[codecov]

Codecov Report

Merging #31898 into dev will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##              dev   #31898      +/-   ##
==========================================
- Coverage   94.69%   94.68%   -0.01%     
==========================================
  Files         763      763              
  Lines       55181    55183       +2     
==========================================
- Hits        52252    52251       -1     
- Misses       2929     2932       +3

Impacted Files	Coverage Δ
homeassistant/components/homeassistant/scene.py	93.89% <100%> (+0.09%)	⬆️
homeassistant/components/template/cover.py	96.34% <0%> (-1.37%)	⬇️

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