Add new component value to extension source

For extension source, we are adding a new value to track component
extensions which was previously marked as "external"; this allows for
differentiation between potentially dangerous side-loaded extensions and a false positive.

Bug: 379715001
Change-Id: I81f9b86f0cfb0a25c5f5f49a06262f1fd68732d0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6488650
Commit-Queue: Haihan Chen <haihan@google.com>
Reviewed-by: Dominique Fauteux-Chapleau <domfc@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1452689}