Offer prefill requests to Change password forms

That should increase the data that we have and hence get more insights
and work on appropriate improvements. This is currently disabled behind
a flag and shouldn't be enabled before launching the main experiment to
100% stable.

Change-Id: I4cc0c4eae51a9213e57dfc936441a9c180cd1f66
Bug: 331757948
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5401846


Reviewed-by: Jan Keitel <jkeitel@google.com>
Commit-Queue: Sayed Elabady <elabadysayed@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1281768}