[buildbucket] Serve 25% of batched/unbatched prod ScheduleBuild requests
[buildbucket] Serve 25% of batched/unbatched prod ScheduleBuild requests

Bug: 1042991
Change-Id: I0e4ceb980e97de26b0855187d9bec92cbecdfd39
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/3099069
Reviewed-by: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@google.com>
Commit-Queue: smut <95deb7aa15d4c615299e47e7688551456568b1fb@google.com>

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