Store creation M2: show store summary after store creation success

[jaclync]

Part of #8106
⚠️ Please only review this PR when the base PR #8107 is approved without critical suggestions

Description

After domain selection and before IAP, we need to create a free site and then pass the site ID for purchasing the eCommerce plan via IAP. This PR integrates the site creation backend and UI, where the tap to continue a selected domain triggers the site creation API request and shows a spinner in the CTA at the same time. After site creation success, StoreCreationCoordinator navigates to a new screen added in this PR, StoreCreationSummaryView, wrapped in a hosting controller. In case of site creation failure, an error alert is shown (we can polish the error state later).

Testing instructions

• Log in if needed
• Go to the Menu tab, and tap Switch store
• On the store picker, tap + Add a store
• Tap Create a new store --> the domain selector should be shown
• Enter some valid query for domain suggestions
• Select a domain and tap Continue --> after a bit, the store summary screen should be shown as in the screenshots

Screenshots

I tested the domain error path by hard-coding the domain to be an empty string in the site creation request.

domain selector	creating store	store summary	domain error

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• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

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[itsmeichigo]

LGTM 🚢

[itsmeichigo]

Nit: we can also add an @available attribute here to signal the compiler in compile-time that this initializer is not ready for use:

Suggested change

	required dynamic init?(coder aDecoder: NSCoder) {
	@available(*, unavailable)
	required dynamic init?(coder aDecoder: NSCoder) {

[jaclync]

Nice, updated in b0b8bf9