feat: improve headers guideline (#769)

[tkrop]

This pull request picks up a couple of header related tasks and left overs from previous pull request, e.g. #760, and from the rolling agenda to complete default header definition support via the guidelines:

• Add general introduction on how to reference default header definitions from the guideline.
• Add script to generate guideline definition of headers from provided default models to use models as a single source of truth.
• Add support for Idempotency-Key, Prefer, Accept-Encoding, Content-Encoding, Sunset, and Deprecation headers.
• Improve support and correct definitions of If-Match, If-None-Match, ETag , Cache-Control, and Vary headers.
• Replace references to RFCs obsoleted by RFC-9110 and RFC-9111 - except of status code and error codes section.

Generally, this pull request is editorial and does not require Zally to be changed, however, it would be good to add a hint about compression as a Zally rule, since we now can identify endpoints not supporting compression.

[tfrauenstein]

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[tfrauenstein]

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[tkrop]

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