[iOSKAUpgrade] Add empty state header to manual fill payment table view

This CL displays the "No payment methods found" message in the payment method manual fill view when the Keyboard Accessory Upgrade feature is enabled and there a no payment method suggestions to show.

UI with the feature on:
https://screenshot.googleplex.com/At4mh4eZPFrjqkR.png

Mocks: go/ios-keyboard-accessory-upgrade-mocks

Fixed: 328089395
Change-Id: I114919ab632ad95c6143731c046d6512807a29ce
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5324149
Reviewed-by: Tommy Martino <tmartino@chromium.org>
Commit-Queue: Noémie St-Onge <noemies@google.com>
Cr-Commit-Position: refs/heads/main@{#1269211}