Integrate gitlab-ci/keep_artifacts

Commit: seco-ne/yocto/infrastructure/gitlab-ci@de9851be

ci: add a job to handle artifacts after merge

In the latest commit in the manifest it often happens, that the pipeline does not contain the artifacts itself, but just a link to the pipeline of the MR.

Added a python script with corresponding GitLab CI job to launch this script. The script searches for the latest pipelines for default branch in manifest repo, and then decides either to keep or delete artifacts for particular build.

The build artifacts are kept for:

• the latest commit
• the last successful build
• the tagged commits (e.g. "fngsystem/47.0", "kirkstone/20.0")

.gitlab-ci

-Subproject commit 1299a9d671826104a620e4b2fd8ce278dd306987
+Subproject commit de9851beff4cbb43172bc3e2ad4709f8d9e00790