ci: Enable images build and Yocto layer check

Major changes:

* Update utility-image for supporting image build
* Introduce kronos-build.yml which extends kas_build, to complete
  image build and other kas build related jobs
* Introduce kronos-image-builds.yml to include fvp-rd-kronos baremetal
  in the list of images to be built
* Introduce image_build.yml.j2 template for generating the image build
  child jobs
* Introduce yocto-qa.yml for Yocto layer check
* Introduce trigger-image-builds.yml to merge jobs and trigger them
* Add and update rules for new jobs
* Add auxiliary scripts, including:

  * jobs-to-kas
  * update-repos.py
  * converting yoctoqa result to junit format
  * generating child job test report

Changelog: other
Signed-off-by: Robbie Cao <robbie.cao@arm.com>
Signed-off-by: Jingzhao Ni <Jingzhao.Ni@arm.com>