[battery] Add missing owners in //chrome/browser/metrics/power/

Change-Id: Iee2654bfbfa321c9249de4785edbe6549532ba6e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2615819Reviewed-by: Sébastien Marchand <sebmarchand@chromium.org>
Commit-Queue: François Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#841183}

chrome/browser/metrics/power/OWNERS

 etiennep@chromium.org
 fdoray@chromium.org
 olivierli@chromium.org
+pmonette@chromium.org
+sebmarchand@chromium.org