Update version to 1.0.8 and add Airlabs flight details integration

[WickedGhost]

This pull request introduces an optional integration with the Airlabs Flight API, allowing users to fetch detailed flight information in addition to the existing Avinor data. It adds a new service for retrieving flight details, updates configuration options and documentation, and includes supporting code and test stubs for improved maintainability and usability.

Airlabs Flight API Integration:

• Added AirlabsApiClient class to api.py for fetching detailed flight information from the Airlabs API, with error handling and parameter validation.
• Introduced a new service get_flight_details (with schema and documentation in services.yaml) to fetch flight details using the Airlabs API, supporting both configured and per-call API keys. [1] [2]
• Registered and removed the service dynamically based on integration setup/unload, ensuring clean resource management. [1] [2]

Configuration and User Experience:

• Updated configuration flow to allow users to optionally provide an Airlabs API key during setup or options editing. [1] [2] [3] [4]
• Extended const.py with new constants for Airlabs integration and service naming. [1] [2]

Documentation and Metadata:

• Updated README.md with instructions for the new Airlabs flight details feature, including service usage examples and configuration guidance. [1] [2] [3]
• Bumped version to 1.0.8 in manifest.json to reflect the new feature.

Testing Support:

• Added tests/conftest.py to provide stubs for Home Assistant modules, enabling unit tests to run outside a full Home Assistant environment.
• Updated API test imports to include the new AirlabsApiClient.