[Extensions] Add karandeepb@ as OWNER of webRequest

Karan's been the go-to person for webRequest issues for awhile. Add him
to the ONWERS file. Also add an OWNERS file to
extensions/browser/api/web_request (and have the //chrome one point to
that).

Bug: None
Change-Id: Iaac56b50c305238e99c2e033ce710c05c0847860
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1612023Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#659600}

chrome/browser/extensions/api/web_request/OWNERS

-battre@chromium.org
+file://extensions/browser/api/web_request/OWNERS
+
+# COMPONENT: Platform>Extensions>API

extensions/browser/api/web_request/OWNERS

+karandeepb@chromium.org
+battre@chromium.org
+
+# COMPONENT: Platform>Extensions>API