Stepper: Reset new-hosted-site-flow store when mounting the flow

[epeicher]

Related to DOTOBRD-12-linear-issue

Proposed Changes

• Refines the condition to reset the OnboardStore when mounting the new-hosted-site-flow

Why are these changes being made?

• To fix an issue with sharing the state when having multiple tabs open at the same time
• The partnerBundle piece of state was being read from the new tab when it should not be there for a new flow

Testing Instructions

• Apply these changes and run Calypso locally
• Navigate to the PTO flow /setup/new-hosted-site/plans?partnerBundle=square
• Check the partnerBundle is in the state by running window.wp.data.select('automattic/onboard').getPartnerBundle() in the Developer Console
• Without closing the tab, open another tab and navigate to the flow without the partnerBundle, i.e. /setup/new-hosted-site (please note that /plans should not be added).
• Check the partnerBundle is not in the state by running window.wp.data.select('automattic/onboard').getPartnerBundle() in the Developer Console
• Complete the flow to create a site without the partnerBundle
• Check the WooCommerce plugin is not installed
• Complete the flow in the tab with the partnerBundle
• Check the system navigates to WooCommerce Launchpad and Get paid with Square is displayed

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 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:commit-b5fa395879c0281aa5f0f448fa43345d4e308cf3

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:commit-b5fa395879c0281aa5f0f448fa43345d4e308cf3&env=jetpack

Automattic for Agencies live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:commit-b5fa395879c0281aa5f0f448fa43345d4e308cf3&env=a8c-for-agencies

[matticbot]

This PR does not affect the size of JS and CSS bundles shipped to the user's browser.

Generated by performance advisor bot at iscalypsofastyet.com.

[gavande1]

LGTM !