devserver: Support update payload metadata for full_payload artifact

BUG=chromium:403086
TEST=devserver_integration_test.py

Change-Id: Iad49f87c9ed79327f1eb5f4b03648f28110f4f15
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/1826048
Tested-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Achuith Bhandarkar <achuith@chromium.org>
Commit-Queue: Amin Hassani <ahassani@chromium.org>
4 files changed