[resultdb] Add definitions for the Go API of ResultSink.
[resultdb] Add definitions for the Go API of ResultSink.

Bug: 1017288
Change-Id: I40780221a11550bb999ceab7fe45848fd8b45c71
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/1880442
Commit-Queue: Sajjad Mirza <47fd465f34da12b7fdcc2312473b40d4ef838af7@chromium.org>
Reviewed-by: Nodir Turakulov <ef4933a197ef7b4b3f55f1bec4942aead3637a2a@chromium.org>

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