[buildbucket] logDetails only for not-onboarded RPCs
[buildbucket] logDetails only for not-onboarded RPCs

The memory profiler shows that much of the memory allocation is
from the Debugf().

Change-Id: Id84136cdf393b8c661e33997b6cd8ac7485f3025
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/2721365
Commit-Queue: Scott Lee <1dcb292530f82960316cb3d87cd67c3f212b79cb@chromium.org>
Reviewed-by: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>
Reviewed-by: smut <95deb7aa15d4c615299e47e7688551456568b1fb@google.com>
Reviewed-by: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@google.com>

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