Add button to go back to tracking view from dashboard listing

What does this MR do and why?

Related to Add button to go back to tracking view from das... (#383342 - closed) and Follow-up: Lazy load the product analytics quer... (#384567 - closed)

On Onboarding - tracking codes view (!106771 - merged), we created the Onboarding setup page. This MR makes it accessible from the dashboards list page by redirecting to it and showing copyable keys for reference in a dropdown. It also lazy-loads a few routes (including the one introduced here).

Screenshots or screen recordings

Click to expand dashboard list screenshot

Click to expand setup page screenshot

How to set up and validate locally

Please follow the instructions at https://gitlab.com/gitlab-org/gitlab/-/snippets/2474959 to enable Product Analytics on your GDK.

With the Product Analytics feature enabled:

1. Go to /gitlab-org/gitlab-shell/-/product_analytics/dashboards or any other instrumented project.
2. The "Instrumentation details" dropdown should be at the top of the dashboards list.
3. The "Instrumentation details" dropdown should show the two copyable keys (SDK Host and SDK App ID).
4. Clicking "Instrumentation details" should redirect to the setup page. The "Back to dashboards" button should be at the top of the page.
5. Clicking "back to dashboards" should redirect to the same dashboards page.
6. The setup page should be accessible by appending /setup to the dashboards route (/-/product_analytics/dashboards/setup).

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.