[Web Payment] SPC enrollment clientDataJSON.type is "payment.create"

Before this patch, enrolling into SPC returned a PaymentCredential with
"webauthn.create" type in clientDataJSON.

This patch changes the clientDataJSON.type to "payment.create".

After this patch, if SecurePaymentConfirmationAPIV2 flag is enabled,
enrolling into SPC returns a PaymentCredential with "payment.create"
type in clientDataJSON.

Bug: 1210488
Change-Id: I28da8da2d52ce46a68cc945204d5a04110ac193e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2976282
Commit-Queue: Rouslan Solomakhin <rouslan@chromium.org>
Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#895306}