Staging sites: Add track events for adding staging site

[katinthehatsite]

Part of DOTCOM-14324

Proposed Changes

This PR adds track events for the staging sites for when they are created. They are also available in the interim dashboard.

Why are these changes being made?

The new dashboard is missing these two track events.

Testing Instructions

• Pull the changes from this branch
• Open Calypso and then run localStorage.setItem( 'debug', 'calypso:analytics*' ); in the browser console. It might be necessary to reload the page for it to pick up the new localStorage item.
• Ensure that you have an Atomic site
• Navigate to /v2/sites/{yourAtomicSite}
• Use Add staging site button in from the environment switcher
• When you click on the button to add a staging site, you should see this event recorded:

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• Have you written new tests for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• Have you tested accessibility for your changes? Ensure the feature remains usable with various user agents (e.g., browsers), interfaces (e.g., keyboard navigation), and assistive technologies (e.g., screen readers) (PCYsg-S3g-p2).
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the "[Status] String Freeze" label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
  • For UI changes, have we tested the change in various languages (for example, ES, PT, FR, or DE)? The length of text and words vary significantly between languages.
• For changes affecting Jetpack: Have we added the "[Status] Needs Privacy Updates" label if this pull request changes what data or activity we track or use (p4TIVU-aUh-p2)?

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-154611

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-154611&env=jetpack

Automattic for Agencies live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-154611&env=a8c-for-agencies

[matticbot]

This PR modifies the release build for the following Calypso Apps:

For info about this notification, see here: PCYsg-OT6-p2

• help-center

To test WordPress.com changes, run install-plugin.sh $pluginSlug fix/add-track-events-for-adding-staging-site-new-dashboard on your sandbox.

[ivan-ottinger]

Looks great! The event gets tracked correctly:

[gcsecsey]

LGTM and works great, I can see the event firing. 👍