Schemas: Update schema to use JSON v2020-12 and validation

[natalialuzuriaga]

Problem

Currently, the metaschema of code.json follows JSON schema v4. We would like to use JSON schema v2020-12 since this is the official standard. We would also like to add validation functionality features that comes with it.

Solution

• Updated schema (both gov and CMS schemas) to use JSON v2020-12
• Added minimum validation to ensure a 0 minimum for numeric fields
• Added uniqueItems: true to ensure no duplicates for arrays
• Updated usage of additionalProperties for all object fields
• Updated tests accordingly
• CMS schema: Removed upstream field since SBOM is now in play

[decause-gov]

LGTM +1 🚢