Referential integrity should be checked

[dtuite]

There are cases where a Backstage metadata file will fail to import because of a group or other dependency that doesn't exist.

For example, if Group:engineering doesn't exist in the Backstage instance we try to import this YAML into, the import will fail.

apiVersion: backstage.io/v1alpha1
kind: Component
metadata:
  name: sample-service-1
  description: A service for testing Backstage functionality
  annotations:
    github.com/project-slug: RoadieHQ/sample-service
spec:
  type: service
  owner: Group:engineering
  lifecycle: experimental

The validator should detect these failures as part of its standard suite of checks.

[roadie-bot]

https://app.shortcut.com/larder/story/5575

[cal5barton]

It should also follow the targets for kind: Location