[server] Log unrecognized requests.
[server] Log unrecognized requests.

R=iannucci@chromium.org, nodir@chromium.org, tandrii@chromium.org

Change-Id: I337a6a5eb2739f98bbdee47d947cd0f7fa10f608
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/1922940
Reviewed-by: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@google.com>
Commit-Queue: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>

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