gitlab-ci: Accept $BUILD_ID CI var to create additional tags

When triggering a pipeline, by setting the BUILD_ID CI variable it is now possible to tell the pipeline to create $IMAGE:$BUILD_ID tags like v2022dev0-image-builder:20201225.000.

With this it is possible to have an external orchestrator trigger all the nightly pipelines with a shared build id, rather than have each pipeline compute one at different times.

• Normal pipeline: https://gitlab.apertis.org/infrastructure/apertis-docker-images/-/pipelines/163599
• Pipeline setting BUILD_ID: https://gitlab.apertis.org/infrastructure/apertis-docker-images/-/pipelines/163600

changed the description

added 2 commits

• 4bedb273 - 1 commit from branch apertis/v2022dev0
• 882bbd76 - gitlab-ci: Accept $BUILD_ID CI var to create additional tags

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enabled an automatic merge when the pipeline for 882bbd76 succeeds

merged