Jetpack Partner Portal: add the feature flag and required modules for a page to create a WP.com site

[yashwin]

Closes https://github.com/Automattic/jetpack-avalon/issues/47

Proposed Changes

This PR adds the feature flags and required modules for a page to create a WP.com site.

Testing Instructions

• Open the Jetpack Cloud live link
• Append the URL with /partner-portal/create-site and verify the below screen is shown.

• Verify that the jetpack/pro-dashboard-wpcom-atomic-hosting feature flag is enabled only in Dev and Horizon environments and not in Staging & Production.

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 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 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-ajp-p2)?

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-78736

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-78736&env=jetpack

[matticbot]

Here is how your PR affects size of JS and CSS bundles shipped to the user's browser:

Sections (~51 bytes added 📈 [gzipped])

name                          parsed_size           gzip_size
jetpack-cloud-partner-portal       +404 B  (+0.1%)      +51 B  (+0.0%)

Sections contain code specific for a given set of routes. Is downloaded and parsed only when a particular route is navigated to.

Legend

What is parsed and gzip size?

Parsed Size: Uncompressed size of the JS and CSS files. This much code needs to be parsed and stored in memory.
Gzip Size: Compressed size of the JS and CSS files. This much data needs to be downloaded over network.

Generated by performance advisor bot at iscalypsofastyet.com.

[jkguidaven]

The new page loads correctly. I have a non-blocking comment, but this is good to go. 👍