Full data model for WebAPI and results tables

[mark-velez]

Discussions around the WebAPI and results data model (i.e. on github, on the wiki, in the forums, but particularly in-person) are confused by our lack of a single, definitive resource describing its structure. Our reconsideration of how the structure gets materialized notwithstanding, can we arrive at a way to include in this repo a representation of the final resulting data model?

Perhaps one of the following could be done automatically by the build:

• a file for each supported db with the full DDL is saved in the resources folder (does flyway support this?)
• webapi_entity_relationship_diagram.png referenced by README is generated

[anthonysena]

Noting this for consideration in the 2.8 release. Also tagging @leeevans @chrisknoll @pavgra @fdefalco to see if they have any ideas on how this type of documentation might be automatically created either by Flyway or some other process that could run during a CI pipeline.