Add the possibility to presave the generated password as backup

The method's goal is similar to the PresaveGeneratedPassword, except we
don't want to create a different credential for the generated password.
Instead, the password will be stored within the credential used to login
to the site.

Bug: 411069395
Change-Id: I1cbd60ec7c17d9a6c55cc9c2d1361669b4b10130
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6573556
Commit-Queue: Oleksandr Tara <otara@google.com>
Reviewed-by: Maria Kazinova <kazinova@google.com>
Reviewed-by: Vasilii Sukhanov <vasilii@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1469825}