Clarify requirement for 3D Secure in sandbox accounts

With this change, we are explaining in the UI that 3D Secure is not available
in sandbox accounts despite being a requirement for some card types.

This is needed because the normal hint displayed on production for cards that
require 3DS, would link users to a page that is not available on sandbox
accounts.

Further information in JIRA.

https://payments-platform.atlassian.net/browse/PP-12593

app/controllers/payment-types/get-index.controller.js

@@ -27,7 +27,10 @@ function formatCardsForTemplate (allCards, acceptedCards, threeDSEnabled) {
 
       if (card.requires3ds && !threeDSEnabled) {
         formatted.disabled = true
-        formatted.hint = {
+        formatted.hint = process.env.NODE_ENV !== 'production' ? {
+          html: `3D Secure, required to accept ${card.label}, is not available in Sandbox accounts.`
+        } :
+        {
           html: `You must <a class="govuk-link" href="/3ds">enable 3D Secure</a> to accept ${card.label}`
         }
       }