Add support for defining a default build profile

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Describe the request

Implement the "Using a default profile" component of the "Sketch build profiles and reproducible builds" RFC.

Describe the current behavior

The majority of the "Sketch build profiles and reproducible builds" RFC has now been implemented (https://github.com/arduino/arduino-cli/pull/1713).

One missing part is the support for the default_profile key of the sketch project file.

🙁 There is currently no way to define a default profile, to be used when the arduino-cli command operating on a sketch with build profiles does not contain a --profile flag.

Arduino CLI version

0.23.0

Operating system

All

Operating system version

N/A

Additional context

Issue checklist

• [X] I searched for previous requests in the issue tracker
• [X] I verified the feature was still missing when using the latest nightly build
• [X] My request contains all necessary details