Package v6

[jormaechea]

Issue to discuss, follow up and document migration for all the breaking changes for package v5.

Breaking changes:

• Add serverless handler like in event listener package, removing current dispatcher that loads API in file structure following the API path
• Change superstruct for @janiscommerce/superstruct and validate properly dates and objectIds.

New features

• Unify ApiList, ApiGet and ApiSave in this package

Must-have third party updates

• API Test major to test serverless handlers instead of classes (just like event listener test)
• Janis CLI major to generate API files properly