pipeline: build workloads in parallel

[huanjani]

Our pipelines deploy workloads in parallel by default, but they could also build in parallel to save time.

Customer request: https://stackoverflow.com/questions/72375124/is-it-possible-to-make-the-build-stage-parallel

We could possibly use this CodeBuild feature: https://stackoverflow.com/questions/72375124/is-it-possible-to-make-the-build-stage-parallel