[Extensibility] [twenty-sdk] [v2] Use twenty-sdk classes to define application entities

[martmull]

• create a twenty-sdk
• add BaseWorkspaceEntity type in the twenty-sdk
• when creating an application, when creating a new object, user should create a new file application/objects/newObject.ts
  This file contains a class New Object that extend BaseWorkspaceEntity
• the twenty-cli should create the manifest.json based on those BaseWorkspaceEntity definition classes