Integrate gitlab-ci/use-parent-child-build-jobs

Commit: seco-ne/yocto/infrastructure/gitlab-ci@2e6c1b4f

Build jobs: Use parent-child jobs to generate needed build jobs

• Move all build, deploy and test stubs to the manifest-build.yml
• Create a new job to generate and trigger the build jobs dynamically
• Add the base jinja2 file for the build jobs.
• Add initial docs for the manifest pipeline
• Remove unused files