[CICD] Add Clea OS gitlab-ci and 'layers-integration' steps
This is necessary to perform automatic commit SHAs integration in 'meta-seco-clea-os' SRCREV.conf file enabling the process described in this part of the documentation: https://git.seco.com/clea-os/infrastructure/gitlab-ci/-/blob/master/docs/automatic-layers-integration.md?ref_type=heads