DevOps Adoption - Replace mocked data with fixtures

The following discussion from !66602 (merged) should be addressed:

• @mrincon started a discussion:

  Suggestion (non-blocking): Keeping mock data manually up to date can lead to mistakes and integration problems. I suggest switching to fixtures in the next MR.

  https://docs.gitlab.com/ee/development/testing_guide/frontend_testing.html#graphql-query-fixtures