#6336606 Domains: Show “Get Domain Card” even if paid user does not have free domain credits anymore

Changes proposed in this Pull Request

In the context of the domain pages redesign (pcYYhz-e4-p2), we redesigned the layout of the initial site domains management page (Upgrades > Domains) in #54615 – now it shows a large card with buttons for the user to either upgrade to a plan or search for a domain, depending if their account is free or has a plan. However, we missed the scenario when a paid user might have used their free domain credits and does not have any domain in their site; in that case, no card was shown and the page was quite empty (see p1628072768015900-slack-C02FMH4G8 for a bug report). How it looked like:

This PR adds a card for the scenario when a paid user does not have free domain credits anymore and no domains in their site. This is how it will look like:

Testing instructions

Use the live Calypso link and select a site with a paid plan but with no free domain credits available and no domains in it. Access the Upgrades > Domains page and ensure the “Add your domain” card is shown.