Added tier visibility to portal tier data

refs https://github.com/TryGhost/Team/issues/1387

We are moving away from using portal products/plans settings to visibility property on the tier object.

core/server/services/members/middleware.js

@@ -112,6 +112,7 @@ const getPortalProductPrices = async function () {
             benefits: product.benefits,
             active: product.active,
             type: product.type,
+            visibility: product.visibility,
             prices: productPrices
         };
     }).filter((product) => {