Part of #8558

Description

For a user to choose a paid domain from WPCOM, I wanted to reuse the pre-existing DomainSelector classes/structs for the free domain selector in the store creation flow. However, a challenge surfaced since the schema of a free domain and paid domain is quite different. For a free domain, we just need to know the domain name. In order to purchase a paid domain, we need to know other info about the domain like the WPCOM product ID. It doesn't make sense to create a protocol for different domain suggestion types, since they are so different. I decided to make the domain suggestion type generic with a protocol for UI display DomainSuggestionViewProperties, and add a protocol DomainSelectorDataProvider for an implementation to return a generic domain suggestion type. There are two implementations, FreeDomainSelectorDataProvider that returns [FreeDomainSuggestionViewModel] and PaidDomainSelectorDataProvider that returns [PaidDomainSuggestionViewModel]. FreeDomainSuggestionViewModel/PaidDomainSuggestionViewModel can then be used to display a domain row.

To integrate the paid domain selector into the domain settings flow, I created a coordinator DomainSettingsCoordinator to navigate to the paid domain selector hosting controller PaidDomainSelectorHostingController when the user taps to add a domain. Sorry for the larger size of the PR than I hoped, it's harder to test the integration otherwise 🙇🏻‍♀️

Please note that there are a few other UI subtasks #8558 for this screen:

• Attributed price info
• Don't show support action in the navigation bar
• Update header text

Testing instructions

Prerequisite: a WC store with a WPCOM plan is required

• Log in if needed, and continue with a WPCOM store
• Go to the Menu tab
• Tap on the settings CTA
• Tap the Domain row
• Tap Add a domain --> domain selector with paid domains should be shown, and each domain should have price info
• Feel free to search for other domains --> each domain should have price info
• Select a domain and tap Continue --> a message about the selected domain should be shown in the console

• @jaclync tests that the free domain selector works as before for store creation

Screenshots

paid domains	free domains

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