Internal release: Make the build_package job to be downstream pipelines

Context

The build_package job on the internal release pipeline takes care of creating the internal packages for the applicable versions (usually two versions). Because we have to wait for the QA jobs on dev.gitlab.org to be available, creating an internal package takes a while, between 25 and 30 minutes.

Considering the long time, creating packages sequentially is not an option.

Transform the build_package from a single job to downstream pipelines

The `internal_release_release:build_package' job should be transformed into a downstream pipeline with two jobs: one job per internal version. These jobs should run in parallel. This approach is similar to the tagging stage of the patch release pipeline where a downstream pipeline with dedicated jobs to tag each version