Studio: Update "Create a free account" link to redirect to magic signup flow

[SiobhyB]

Fixes 5531-gh-Automattic/dotcom-forge and 5532-gh-Automattic/dotcom-forge

Proposed Changes

• Following Redirect Studio app users to magic login flow when signing up wp-calypso#90204, users who choose to create an account from the WordPress.com login page will be redirect to the magic signup flow.
• With this PR, we update the "Create a free account" link in the Studio app to redirect to the new signup flow.

Testing Instructions

• Log out of both WordPress.com and the Studio app.
• In the Studio app, navigate to the Share tab.
• Click on the "Create a free account" link in the Studio app.
• Verify you're taken to the magic signup page and enter an email that's not already associated with a WordPress.com account.
• Go through the flow to complete account setup and verify you're automatically logged into the Studio app.

Link	Form

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

[fluiddot]

LGTM 🎊 ! Awesome work @SiobhyB 🏅 !

I followed the testing instructions and managed to create a new WPCOM account via the magic signup flow. The last step redirected successfully to the page that prompts opening the Studio app and confirmed the new account is logged in the app.

[sentry-io]

Suspect Issues

This pull request was deployed and Sentry observed the following issues:

• ‼️ Error: Can not find Squirrel t.setupUpdates(main/studio/./src/updates) View Issue
• ‼️ Error: Failed to get 'logs' path t.setupLogging(main/studio/./src/logging) View Issue
• ‼️ RangeError: Incorrect locale information provided t.getSupportedLocale(main/studio/./src/lib/locale) View Issue

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