[rts] Warn about cold Gerrit cache
[rts] Warn about cold Gerrit cache

The first evaluation for a given history file is always very slow because
Gerrit info is not cached. Warn about this.

R=tandrii@chromium.org

Bug: 1112125
Change-Id: Ida8101544425af3f847df4979d83f5310f728fc1
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/2448194
Commit-Queue: Nodir Turakulov <ef4933a197ef7b4b3f55f1bec4942aead3637a2a@chromium.org>
Auto-Submit: Nodir Turakulov <ef4933a197ef7b4b3f55f1bec4942aead3637a2a@chromium.org>
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