feat: Allow separate asset upload jobs per environment

[joshbegin]

For security, we require a Github Environment to be specified on a job before allowing it to assume an AWS Role. For example, only a job with environment: qa can assume a role in our QA AWS account.

This requirement prevents the AssetUpload Job from running since there is no "environment" specified. If we use the assetPublishingPerStage property, it tries to change to the appropriate role for each stage (qa, uat, etc...), but, even if we add an environment it will not work since a job can only have one environment.

This PR proposes a useGithubEnvironmentsForAssetUpload boolean property that will allow creation of a separate Job for each stage that can run in parallel and assigns an environment for each job.

[hoegertn]

Hi, I really like the idea of the feature. There is two thing I would like to ask before reviewing the code:

1. We need to explain and document the fact, that splitting the asset stage means rebuilding container assets for each stage and they will not be the "same binary"
2. There are a lot of whitespace changes that make it ahrd to review the code. Any idea where they come from?

[hoegertn]

@joshbegin is this still somethign you would like to tackle?