Proposed change

Adds migration logic to handle config entries created before the CONF_AUTH_TYPE field was introduced in PR #149783. The migration automatically detects the authentication type based on the presence of either CONF_TOKEN (for API token auth) or CONF_USERNAME/CONF_PASSWORD (for password auth) and updates the config entry accordingly.

This resolves the 'Unknown authentication type in config entry' error that users experienced after upgrading to Home Assistant Core 2025.11.0.

Fixes #155906

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)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: Growatt: Unknown authentication type in config entry #155906

Checklist

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