[Android] Set syncable pref for the first plus address creation time.

This CL sets the syncable pref plus_addresses.creation.first.time, when
the user accepts the plus address creation bottom sheet for the
first time, i.e. when the user creates their first plus address.

This pref will be used to attach additional data to the plus address
HaTS surveys.

Bug: 348139343
Change-Id: I709d4d703c706e613b08a6176d4b492ba94d60ae
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5975138
Reviewed-by: Jan Keitel <jkeitel@google.com>
Commit-Queue: Timofey Chudakov <tchudakov@google.com>
Cr-Commit-Position: refs/heads/main@{#1376256}