MANIFEST_PROJECT, MASTER_BRANCH_MANIFEST, MASTER_BRANCH_PROJECT

Using new function raise_if_error() of GitPython 3.1.25:
https://gitpython.readthedocs.io/en/stable/tutorial.html#handling-remotes

This shares YAML code for the following procedures:
- Build environment
- Source code checkout via repo
- SSH key and known hosts setup
- LAVA test submission
- Docker check if build folder is empty

The yamllint job was included in the pipeline implicitly via the
inclusion of common.yml. This is not very transparent. Make the common
definition a base job and extend it explicitly in each pipeline now.

Add infrastructure stage comment header into both yaml files.

This is the first step for reducing code duplicates.

BCS 746-000807

* 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

BCS 746-000808

This makes merging a project MR possible even if the manifest has
received new commits since the MR pipeline build has run. The developer
is responsible for deciding whether it is safe to merge it without
having a build based on the latest manifest.

BCS 746-000794

Also set yocto deploy job to manual to test merge.