fwupd: Implement downloading firmware patch locally

Downloads a firmware patch from a Google-hosted server and stores it
into the device's local tmp directory. The stored patch is applied to
the peripheral with the matching device ID.

Currently downloads from a hardcoded valid URI. Followup will allow
downloading from dynamically fetched URI's.

Bug: 1252981
Test: ash_unittests
Change-Id: I23ec6efdfd632526bbcfd8b21f845a25090e7ffe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3337592
Reviewed-by: Zentaro Kavanagh <zentaro@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Commit-Queue: Jimmy Gong <jimmyxgong@chromium.org>
Cr-Commit-Position: refs/heads/main@{#952266}