Investigate impact of parallel changes for declarative

There is a proposal to clarify how to use parallel with declarative, using stages. This has the benefit of allowing config items that naturally live at stage level to be in parallel branches. This may result in some changes in flownodes/bismuth, and how it works with blue ocean visualisations (functionally things are similar):

A sample here: https://gist.github.com/abayer/bbe18e779696af88af9208f7502b898c

The declarative ticket for this feature: https://issues.jenkins-ci.org/browse/JENKINS-41334
PR https://github.com/jenkinsci/pipeline-model-definition-plugin/pull/98

In scope:

• See what impact (there may be none) is of running declarative pipelines in this style with bismuth and blue ocean
• potentially make api adjustments/requests.