Add relations for unit_primitives

The Config

# config/unit_primitives/code_suggestions.yml
---
name: code_suggestions
description:
cut_off_date: 2024-02-15T00:00:00+00:00
min_gitlab_version_for_free_access:
min_gitlab_version: '16.8'
unit_primitive_issue_url:
introduced_by_url:
documentation_url:
group: group::code suggestions
feature_category: code_suggestions
backend_services:
  - ai_gateway
add_ons:
  - duo_pro1
  - duo_enterprise
license_types:
  - premium
  - ultimate

# config/backend_services/ai_gateway.yml
---
name: ai_gateway
description:
project_url: https://gitlab.com/gitlab-org/modelops/applied-ml/code-suggestions/ai-assist
group: group::ai framework
jwt_aud: gitlab-ai-gateway

# config/add_ons/duo_pro.yml
---
name: duo_pro
description:

# config/license_types/ultimate.yml
---
name: ultimate
description:

Testing locally

Edit YAML files in configuration and run the validate rake job:

bundle exec rake gitlab_cloud_connector:validate:yml

It should fail with the proper error if the configuration is invalid.

related to: #9 (closed)