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