Add Product Analytics to Experiment features list

Proposal

Users will need opt-into the experimental features and add Product Analytics specifically.

Technical proposal

Tidy up the UI for group-level experiment toggle

This was added with AI features in mind, but there's no reason it can't be extended to other features for Ultimate SaaS customers.

• Update https://gitlab.com/gitlab-org/gitlab/blob/master/ee/app/views/groups/settings/_ai_related_settings.html.haml to make it no longer AI specific. It should be license gated, but not just for AI features. Consider adding a new Ultimate feature gate for experimental features.
• Maybe update the i18n namespacing too so that they're not all grouped within AI.

Put product analytics behind Experiment Feature toggle

• With the above in mind, put product analytics behind the new Experiment Features toggle. - !131915 (merged)

Put product analytics behind its own toggle underneath Experiment Feature toggle

This is important because we need a way to disable opt-in into the product analytics feature in case we cannot handle the amount of users already opted in.

Currently, AI features need the Experiment Feature and Third-party AI Feature toggles both enabled, so we can't simply disable the Experiment Feature checkbox to disable product analytics opt-in.

#### Update the existing product analytics functionality

1. Currently, if the correct feature flags are enabled, that's sufficient to use Product Analytics. We need to add in another check that the namespace's namespace_settings.experiment_features_enabled is set to true. If its not, then regardless of the feature flags, the features should be disabled. 2. Once we're ready to launch as an experimental feature, we should remove all of the feature flags and rely solely on the namespace opt-in to experimental features. That comes later; see the note below about use of feature flags.

#### Update the docs

1. Change the Experiment badge to Beta

Note: Crossed out work moved to new issue for upcoming milestone: #425323 (closed)

Constraints

We cannot release this until the Experiment Phase is over / Beta Phase is ready to start, so this ALSO needs to be behind a feature flag. Super meta.

Acceptance Criteria

For the following assume users are Ultimate Customers as both VSD and Product Analytics are only available to Ultimate customers.

Experiment/Beta Toggle	Product Analytics Toggle	Value Stream Dashboard Visibility	Product Analytics Visibility
Off	Off	Analytics Dashboards Left nav displays, Value Stream Dashboard is visible in the list.	Product Analytics settings do not display in Settings, The Default Dashboards are not displayed when Analytics Dashboards is selected.
Off	On	N/A this configuration is not possible.	N/A this configuration is not possible.
On	Off	Analytics Dashboards Left nav displays, Value Stream Dashboard is visible in the list.	Product Analytics settings do not display in Settings, The Default Dashboards are not displayed when Analytics Dashboards is selected.
On	On	Analytics Dashboards Left nav displays, Value Stream Dashboard is visible in the list.	Product Analytics settings are displayed in Settings, The Default Dashboards are displayed when Analytics Dashboards is selected.