fix: allow build on macos via docker

[thoro]

Comprehensive Summary of your change

Add the option to define the platform inside the Makefile, it defaults to linux and the corresponding arch where the Makefile is executed. For macos M1+ that would be arm64 - this requires the arch binary.

This is only intended for testing builds on macos / arm and not for running harbor on mac as a hosting platform

Updated the spectral version to the newest version (6.11.1) which provides an arm64 image.

Issue being fixed

Fixes #20852 #17016 #15928 (and probably others) Improves #19688

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• [x] Made sure tests are passing and test coverage is added if needed.
• [x] Considered the docs impact and opened a new docs issue or PR with docs changes if needed in website repository.