Rename variable JENKINSGUF_SSH_PRIVATE_KEY / SSH_PRIVATE_KEY to
GITLAB_PRIVATE_KEY on this occasion, because it contains a private key
that was generated exclusively for this use case. The according public
key has been added as a deploy key in GitLab to all repositories that
this repository needs access to.

Add more detailed documentation concerning this configurationdirectly in
the gitlab-ci files.

Our settings refuse to merge if no pipeline has been run.

Also set yocto deploy job to manual to test merge.

Integrates the changes done in the foobar- yml files to the yocto
projects.

Create a merged version of the gitlab-ci files from the layers and the
repositoried referenced by the SRCREV file to be included in the
projects, to replace the project-individual implementation.

BCS 746-000646

Also add all yml files to the yamllint check and replaces the project
path check with a more general project-root check.

BCS 746-000646