Implement Plugin Architecture for Whisk Deploy

I dont have lot of information on this topic yet but we would like to move towards plugin architecture so that introducing any new field/entity/extension becomes simpler in terms of preprocessing of YAML keys.

The issue names no files, tests, or entry points. Start by mapping the YAML-key preprocessing flow and identifying how new fields, entities, and extensions are currently introduced. Done means a plugin architecture makes those additions simpler without requiring changes throughout the preprocessing flow.

Written by the indexing model from the issue text.