Validate manifests during populating them into Hub

[pkosiec]

Description

• Validate manifests when populating them to Hub
  • Taking into account current design, it should be probably a part of Populator job
  • Use existing validation logic from the pkg/sdk/manifest package
  • Run also remote checks (make sure the manifest kinds are populated in a proper order, to e.g. verify whether a given Attribute exists for all Implementations)
    • Probably we need another GraphQL endpoint to access unpublished manifests (do we need to generate another GraphQL schema?)

Reason

Manifest validation is an essential feature for productive content development. Content Developer should be rejected immediately on any error found while using Populator to upload the manifests.

Use cases

• As a Content Developer, I want to use Populator knowing, that all manifest issues will be detected immediately.
• As a System Administrator, I want to ensure Capact is properly configured to consume already validated manifests from a given Public Hub.