#4638616 Coming soon: add coming soon page selector

Changes proposed in this Pull Request

This PR splits out the page selector functionality in #45606.

We’re adding a coming soon page selector to the ellipsis menu for sites with a paid plan.

We’re also showing a coming soon badge to indicate that a page has been selected as coming soon.

Testing instructions

Make sure your test site as a paid upgrade, e.g., a personal plan.

Ensure that the new coming soon mode is activated on your test site, e.g.,

wp option --url=your_site add wpcom_public_coming_soon 1

Go to http://calypso.localhost:3000/pages/{your_site}?flags=coming-soon-v2

Assign a site to be your coming soon page

Check that we’re firing the coming soon page set toggle tracks event calypso_coming_soon_set_page:

Check that the badge is assigned

Also make sure the network request to public-api.wordpress.com/rest/v1.1/sites/{site_id}/homepage is fired with the correct page ID:

Refresh the page to check that the page id has been saved. Also run:

wp option --url=your_site get wpcom_public_coming_soon_page_id

Now switch off the feature flag (Go to http://calypso.localhost:3000/pages/{your_site}) and make sure the coming soon ellipsis menu and page badge are not visible.

Repeat the above steps with a free site. You shouldn’t see the coming soon options at all in the ellipsis menu.

Fixes: #45022