Add internal Cluster deployments API for group cluster deployments (BE)

What does this MR do?

Creates a new endpoint for cluster to show environments linked to the cluster. Only for group-level clusters.

To be precise, we only show environments where the last deployment was a deployment to the cluster

CE Port: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/31988

https://gitlab.com/gitlab-org/gitlab-ee/issues/13392

TODO

• ee rollout_status schema test
• Move everything to EE, keep it in group/clusters_controller
• New license attribute that is distinct from :deploy_board - cluster_deployments
• Add new index for deployments#state

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team