Is your feature request related to a problem? Please describe.

Related to #5920.

Using the GitLab REST API can lead to performance issues and hitting rate limits.
Switching to GraphQL could help (we'll need to verify this).

Describe the solution you'd like
Similar to the GitHub backend, having use_graphql: true support for the GitLab backend

Describe alternatives you've considered
Keeping things as they are

Additional context
https://docs.gitlab.com/ee/api/graphql/