Hosting Dashboard Emails: Mailbox selector screen

[mmtr]

Fixes DOTDASH-479
Requires #106524

Proposed Changes

Implements the email provider selection step.

Why are these changes being made?

Because we want to manage emails in the new Hosting Dashboard.

Testing Instructions

• Use the Calypso live link below
• Go to /v2/emails/choose-email-solution/:domain
• Make sure the layout is rendered correctly
• Make sure the prices match what you see in /email/:domain/compare/:site
• Make sure you can switch between monthly and annual subscriptions
• Make sure the Titan free trial is available only if it has not been used before on that domain (you can for instance purchase a Titan upgrade in /email/:domain/compare/:site, then go back to /v2/emails/choose-email-solution/:domain and make sure that the free trial is not offered anymore).

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-159606

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-159606&env=jetpack

Automattic for Agencies live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-159606&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

• blaze-dashboard
• help-center
• notifications
• odyssey-stats
• wpcom-block-editor

To test WordPress.com changes, run install-plugin.sh $pluginSlug dotdash-479-hosting-dashboard-emails-mailbox-flow-select-provider-step on your sandbox.