Change orbit_promo_access_gate flag type to gitlab_com_derisk

What does this MR do and why?

Changes the orbit_promo_access_gate flag type from wip to gitlab_com_derisk, ahead of enabling it on GitLab.com. This type fits a flag that is flipped globally and needs a quick way back, and it requires a rollout issue link, which is now set.

References

• Rollout issue: #633557
• Related to https://gitlab.com/gitlab-org/orbit/knowledge-graph/-/work_items/1354

Screenshots or screen recordings

N/A, no UI change.

Agent context

• Moved the definition from ee/config/feature_flags/wip/ to ee/config/feature_flags/gitlab_com_derisk/, set type: gitlab_com_derisk.
• rollout_issue_url points at the rollout issue above.
• Added log_state_changes: true so flag state logging keeps working once the milestone is no longer upcoming.
• No Feature.enabled? call passes an explicit type:, and nothing else references the old path.
• Specs not run locally (bundle environment not set up in this worktree); the change is YAML-only and the definitions load.