Reland "[BNPL] Add check for externally linked issuer"

This is a reland of commit 1225972dda92f9f7b7f95b2ba15f391c2dce034a.

The test failures related to the reverting are caused by flaky tests.
Same failures happened again without this change (
http://shortn/_Wlg7LpULNE).

Besides, win-asan tests passed with no issue with CQ try runs, and the
flaky tests will be disabled by crrev.com/c/6803424 until the flakiness
is fixed.

Original change's description:
> [BNPL] Add check for externally linked issuer
>
> This CL adds logic to convert sync'ed action required enum for BNPL
> issuer if the corresponding flag is enabled.
>
> Design Doc: go/chrome_bnpl_klarna_desktop_design
>
> Bug: 424259928, b:424600709
> Change-Id: I933215358e7de505bb43096d150b5d86d1183c33
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6776062
> Reviewed-by: Vinny Persky <vinnypersky@google.com>
> Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
> Commit-Queue: Yishui Liu <yishuil@google.com>
> Cr-Commit-Position: refs/heads/main@{#1493007}

Bug: 424259928, b:424600709
Change-Id: Idb801e912e76a943e79f59007aadcee50fb3cbf2
Cq-Include-Trybots: luci.chromium.try:win-asan
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6798918
Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Commit-Queue: Yishui Liu <yishuil@google.com>
Cr-Commit-Position: refs/heads/main@{#1494898}