Add npm as a resource-timing test OWNER, and update team to speed-metrics-dev

Change-Id: Id48f7597a4bd1bbc441e74b02abf1eda9415c1df
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2051007Reviewed-by: Kunihiko Sakamoto <ksakamoto@chromium.org>
Commit-Queue: Annie Sullivan <sullivan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#740508}

third_party/blink/web_tests/external/wpt/resource-timing/OWNERS

-# TEAM: loading-dev@chromium.org
+# TEAM: speed-metrics-dev@chromium.org
 # COMPONENT: Blink>PerformanceAPIs>ResourceTiming
 ksakamoto@chromium.org
+npm@chromium.org