Move GitLab Observability from experiment to beta

What does this MR do and why?

Moves GitLab Observability from Experiment to Beta on GitLab.com and GitLab Self-Managed, targeting 19.5.

• Docs (doc/operations/observability/):
  • Status: Beta on all 8 pages.
  • History entries on observability.md and mcp_server.md.
  • Removed the "experimental feature" framing.
  • Pricing wording changed to "no cost during the beta", because pricing and packaging are still undecided.
• UI (app/views/shared/observability/setup/_setup_page.html.haml):
  • The setup page information row now says Beta / "Beta functionality" / "Free during the beta".
  • locale/gitlab.pot updated to match.
• Feature flag: observability_sass_features moved from experiment/ to beta/ with type: beta.
  • Group corrected to group::embody.
  • Added description, feature_issue_url and the required rollout_issue_url.
  • default_enabled stays false. The flag name is unchanged, so no code references change.

Opt-in is unchanged and still explicit. Each group or personal namespace must select Enable Observability, and there is no automatic enablement path.

Related

• Beta requirements checklist: gitlab-org/embody-team/experimental-observability#3
• Readiness assessment (PREP): https://gitlab.com/gitlab-org/architecture/readiness/-/work_items/119
• Feature flag rollout issue: #632757

Merge conditions

Note

The exception to complete the PREP review after the Beta status change was approved: gitlab-org/embody-team/experimental-observability#3 (comment 3980018964)

Targeting the 19.5 cutoff (2026-10-09). A maintainer other than the author needs to merge this once the pipeline passes.

How to validate locally

1. Enable the flag for a group: Feature.enable(:observability_sass_features, Group.find_by_full_path('<group>')).
2. Go to the group, then Observe > Setup.
3. Confirm the information row shows Beta and Free during the beta.

Checks run

• markdownlint-cli2 and vale on the changed docs: 0 issues.
• Docs link check (lychee): passed.
• spec/lib/feature/definition_spec.rb, spec/requests/{groups,projects}/observability/setup_spec.rb, spec/lib/sidebars/groups/menus/observability_menu_spec.rb: 88 examples, 0 failures.

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist.