[resultdb] Enable prod mode
[resultdb] Enable prod mode

Enable prod mode and pass required flags, in particular root LUCI secret.

Use :gce authentication instead of embedded service account JSON.

R=jchinlee@google.com, vadimsh@google.com

Bug: 1009519
Change-Id: Ica916e6b62261e42515202966f30e4940e841fdc
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/1865951
Commit-Queue: Nodir Turakulov <ef4933a197ef7b4b3f55f1bec4942aead3637a2a@chromium.org>
Auto-Submit: Nodir Turakulov <ef4933a197ef7b4b3f55f1bec4942aead3637a2a@chromium.org>
Reviewed-by: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go