Add Group.dependencyNames GraphQL field

What does this MR do and why?

Related to #454305

Query plans

Cold cache: https://console.postgres.ai/gitlab/gitlab-production-main/sessions/28974/commands/90323

Warm cache: https://console.postgres.ai/gitlab/gitlab-production-main/sessions/28974/commands/90324

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

How to set up and validate locally

query {
  group(fullPath: "<group path>") {
    dependenciesNames {
      id
      name
    }
  }
}