Add change detection rules to skip unnecessary CI jobs

- Add rules to validation jobs (lint_bash, lint_ci_templates, lint_python)
  to only run when relevant source files change
- Upgrade 10 Docker build jobs from exists-only to changes with compare_to
  pattern, so they only rebuild when Dockerfiles actually change
- Add optional: true to all build_docker_dind_image dependencies, allowing
  jobs to run independently when dind build is skipped
- Add scripts/python/** tracking to build_image_remover_image

This reduces pipeline time significantly when only specific files change
(e.g., docs-only changes now skip all jobs).