p13n: improve feedback (5/N) merge two metadata fields

Introduce "from_sea_pen" to stay consistent with "from_mahi" because
Mahi now has its own bucket and does not rely on "from_chromeos"
anymore.

Also move some bucket ID and metadata keys to feedback_constants.h.

Related CL: https://crrev.com/c/5374225

BUG=b:323416428

Change-Id: I742963cc47003019d884625f1446501f5e820446
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5381670
Reviewed-by: Andre Le <leandre@chromium.org>
Commit-Queue: Jerry Liu <pzliu@google.com>
Reviewed-by: Jeffrey Young <cowmoo@google.com>
Reviewed-by: Xiangdong Kong <xiangdongkong@google.com>
Reviewed-by: Darren Shen <shend@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1276549}
NOKEYCHECK=True
GitOrigin-RevId: c233a175363707a49dfbf817347aefb6c7ec6578
6 files changed