[swarming] use CumulativeDistributionMetric for task expiration delay metrics
[swarming] use CumulativeDistributionMetric for task expiration delay metrics

Bug: b/149449699
Change-Id: I7883354484bd21ff950f8efda4ccd1fa246ce4f0
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/2157427
Reviewed-by: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
Auto-Submit: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>
Commit-Queue: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
Commit-Queue: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py