Draft and resolve cross-team concerns in an enhancement for On Cluster Builds. Enhancement should describe main interfaces.

Current working draft may be found here:  [-https://docs.google.com/document/d/1bdWlAtIKbHV_AaM3nllJe_hd3aW-VCUaib7lJJYExlc/edit?usp=sharing-]

PR is live at https://github.com/openshift/enhancements/pull/1515. 

Done When:

• The final draft is reviewed, outstanding open questions are answered, and merged into https://github.com/openshift/enhancements.
• Any additional stories, spikes, etc. are opened and bucketed into the respective Tech Preview and GA epics.