Update CI pipeline to restrict builds and tests to platforms with official LinuxCNC images

[zarfld]

Related to #90

Update the CI pipeline to restrict builds and tests to platforms with official LinuxCNC images and include Raspbian Bullseye with LinuxCNC 2.8-latest.

• README.md:

  • Add a section to document the supported platforms and LinuxCNC versions.
  • Provide instructions for developers on how to replicate the CI environments locally.

• .github/workflows/ci.yml:

  • Update the CI pipeline to restrict builds and tests to platforms with official LinuxCNC images.
  • Include jobs for building and testing each of the required versions (hybrid, PREEMPT-RT, RTAI, and USPACE).
  • Add a job for Raspbian Bullseye with LinuxCNC 2.8-latest.
  • Ensure the matrix includes LinuxCNC versions 2.9.2, 2.9.3, and the latest release.

• create_images.sh:

  • Modify the script to include the creation of images for Raspbian Bullseye with LinuxCNC 2.8-latest.
  • Ensure the script follows the structure and format of existing LinuxCNC releases.
  • Add steps to test and validate the generated images using QEMU.

• BuildLinuxCnc.sh:

  • Modify the script to include support for Raspbian Bullseye with LinuxCNC 2.8-latest.
  • Ensure the script handles the dependencies and configurations required for this environment.
  • Add steps to test and validate the generated images using QEMU.

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For more details, open the Copilot Workspace session.