This is a premium feature available with Astra Pro.
Make sure you have activated the module from Appearance > Astra > Addons > Spacing.
You will get options to set spacing for posts and pagination on blog/archive pages. You can find settings under Appearance > Customize > Layout > Blog > Blog / Archive.
Below are the available options-
Post Pagination Space
It will add a padding around the pagination option from all sides.
Post Outside Space
It will add margin to the individual post from all sides.
Post Inside Space
It will add padding for the individual post from all sides.