LP#2057948: Add Idempotency-Key to prevent duplicate stripe requests

LP#2057948: Add Idempotency-Key to prevent duplicate stripe requests

* Create key from sorted list of transaction IDs passed through md5_hex.
* Do not include xact param for now, since I am not sure what it is;
  xact_misc is the list of transaction IDs selected in the payment form.
* Pass header through -ua_args option when constructing the Stripe obj,
  because the per-request method is not published yet to CPAN.

Tested with manual code on Ubuntu 22 LTS and Business::Stripe 0.07.

Release-note: Adds idempotency to Stripe to prevent duplicate payments

Signed-off-by: Ken Cox <kenstir@gmail.com>
Signed-off-by: Michele Morgan <mmorgan@noblenet.org>
Signed-off-by: Terran McCanna <tmccanna@georgialibraries.org>