Run E2E tests when an MR changes a feature flag YAML file

Proposal

When an MR includes a file in config/feature_flags/development, extract the feature flag from that file and run package-and-qa with the flag enabled and disabled.

• Use the GITLAB_QA_OPTIONS environment variable as a CI variable that is passed to gitlab-qa pipelines via omnibus-gitlab
  • GitLab changes: gitlab-org/gitlab!68814 (merged)
  • GitLab QA changes: gitlab-org/gitlab-qa!744 (merged)
  • omnibus-gitlab changes: gitlab-org/omnibus-gitlab!5573 (merged)
  • Changes to enable use in LDAP scenarios: gitlab-org/gitlab!70038 (merged)
  • Run the tests when a feature flag config file is deleted

Part of https://gitlab.com/gitlab-org/quality/team-tasks/-/issues/782