Create a schema to store vulnerability and package metadata serialized in a suitable JSON (or YAML) format #10

To document the data format, we need to create and publish a schema used to store vulnerability and package metadata serialized in a suitable JSON (or YAML) format.

We could use pydantic and cattrs for this, or generate this from Django models or API definitions.

See some related issues:

• Create "data dictionary" for all SCTK fields and schema scancode-toolkit#2008
• Feature: documentation on json and json-pp formats scancode-toolkit#2826
• Document the structure of ScanCode's JSON output scancode-toolkit#617