[BNPL] Refresh issuers on pref change

This CL ensures that toggling on/off the Pay Over Time settings toggle
will appropriately update the displayed payment methods.

Before: http://shortn/_2Cm2MTfXGo
After: http://shortn/_5LvVG5rFKH

Bug: 356443046, b:398958544
Change-Id: I23f9d231e22dc5e25bda5e46a4d1f2bd9b972329
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6306649
Reviewed-by: Vinny Persky <vinnypersky@google.com>
Commit-Queue: Wilson Low <wilsonlow@google.com>
Reviewed-by: Slobodan Pejic <slobodan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1429563}