Local bricks: aupport app-local inside arduino-app-cli

[Xayton]

An app-local brick:

• is a custom brick that is found in the bricks sub folder of the app
• has all the files and structure of the existing embedded bricks
• can be referenced from the app.yaml file using its ID (found in brick_config.yaml)

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• Add discovery of the bricks inside an app
• Add support when launching an app:
  • the brick compose file must be integrated when launching an app
  • the Python code must be accessible by the Python main container (by mounting the brick Python folder?)
  • install the requirement.txt file of the brick in the Python main container See Local bricks: add support for requirements.txt #206