[Dashboards as code] Decouple from content management #241368
Description
Due to its reliance on the content management system the Dashboard API has one extra layer of abstraction which makes dealing with our types, endpoints and code difficult. We should remove our reliance on content management and instead use the saved objects client directly from our REST endpoints.
Additionally, content management has architecture in place to support up and down transforms when versions change. We should remove this code, as it will not be used until / unless a breaking change is required for the Dashboards API after Tech Preview / GA.