Add warning to custom integrations without version

[ludeeus]

Breaking change

Custom integrations now require a version key in their manifest file, this also means that all custom integrations now require a manifest file.

If you are using a legacy custom integration like custom_components/awesome.py this now needs to move to custom_components/awesome/__init__.py so you can add custom_components/awesome/manifest.json to it.

For more information about integration, manifests have a look here https://developers.home-assistant.io/docs/creating_integration_manifest

For now, this will create a warning on startup. But this will eventually be blocked from loading if it's missing a version in the manifest.

Proposed change

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:

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To help with the load of incoming pull requests:

• I have reviewed two other open pull requests in this repository.

[ludeeus]

It's not working for legacy integrations, marking as draft until that is solved.