Provide a default config file for Clippy

[xFrednet]

We have a few lints with configuration values, like borrow_as_ptr. We want to increase the visibility of these config values, to encourage the use of them.

As part of this, we'd like to provide a default configuration file. The config should be included in the book.

Tasks:

• Examine config values and determine which are probably often used
• Some less commonly used but important ones should be listed, but commented out.
• Additionally, a configuration could be provided, that should be run once before a release with configs like: avoid-breaking-exported-api

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cc: #9880