Gift Card Balance Checker

[brettflorio]

A drop-in "gift card balance checker" element should allow a merchant/dev to easily drop in a widget to their site that allows customers to enter a gift card code, and see the balance and (if applicable) expiration date.

Some notes:

• Must include hCaptcha. I think this should be required always, to prevent brute force / enumeration attacks.
• Return balance and expiration.
• Review how gift cards handle currencies, and output that as well if necessary.
• TBD: Determine where the endpoint lives. (/s/customer/* or /s/*)