Migrate to OpenCHAMI image-thrillhouse

[SAYUK09]

This PR migrates the OpenCHAMI image building pipeline from the legacy image-builder to the new image-thrillhouse tool.

Key Changes:

• Container Image: Switch from dellhpcomniaaisolution/image-build-el10:1.2 to ghcr.io/openchami/image-thrillhouse:latest
• Config Schema: Update image config YAML templates to match image-thrillhouse format:
  • Restructure options → meta and layer sections
  • Convert repo definitions to inline file content format
  • Update package installation syntax
  • Convert command execution to script format
• Build Command: Change from image-build to image-thrillhouse build

Testing:

• Verified RHEL compute image builds successfully with image-thrillhouse
• Successfully PXE booted Slurm controller and one compute node