This will add a coming soon category to the bottom of the starter page templates available on the new page screen.
Part of #45689
Note: currently this card is relatively difficult to test locally because when testing in your sandbox:
The list of all templates is loaded from php code in class-starter-page-templates.php#213
Because this code runs on the server, your hosts file will not be used, it will load the list of all templates from the production public-api.wordpress.com.
Therefore the new coming soon page will not be included in the results.
However it is possible to test locally like so:
Checkout this branch
Set up wp-env following the instructions here: PCYsg-ly5-p2
In another terminal tab, sync the api portion of this code change to your sandbox with yarn dev --sync