Put product analytics toggle behind a FF

We should put the newly added product analytics toggle behind a feature flag so that we can disable product-analytics opt-in during beta if we encounter issues.

Proposal

1. Create a new feature flag product_analytics_beta_optin
2. Check the feature flag value when showing the new toggle in the group settings page
3. Check the new feature flag value when hiding/showing the project level product analytics settings
4. Check the new feature flag to decide whether to take the toggle value into account when showing product analytics dashboards / onboarding

Acceptance criteria

The following scenarios assume

• product_analytics licensed feature is available
• product_analytics_dashboards feature flag is enabled

new feature flag	product analytics toggle	toggle visibility	project level product analytics settings visibility	builtin dashboards / onboarding
disabled	disabled	hidden	hidden	hidden
disabled	enabled	hidden	hidden	hidden
enabled	disabled	visible	hidden	hidden
enabled	enabled	visible	visible	visible