[luci-config] Config service uses project scoped service accounts.
[luci-config] Config service uses project scoped service accounts.

Config service using project scoped service accounts to check access
LUCI config repositories.

Bug: 950683
Change-Id: I49ca4f7f111aae1f861e2d797258969453b203cd
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/1593943
Commit-Queue: Felix Matenaar <6f9f11a7d9d9f9d70470ce23ff837316447e1df6@chromium.org>
Reviewed-by: Nodir Turakulov <ef4933a197ef7b4b3f55f1bec4942aead3637a2a@chromium.org>

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py