Add payment handler test case

[christhompson]

To test URL display in Payment Handler UIs, it would be nice to have a test case that allows us to:

• Register a payment handler with an arbitrary target URL
• Payment handler page should load the page with the list of test URL links (to test loading those URLs in the payment handler UI)

We could also potentially allow arbitrary URL navigations from the page (i.e., text input for URL to redirect to) to make it easier to test edge cases that aren't already in trickuri's corpus.

[ONKARBH]

if you dont mine i will work on this project