[node_preamble] Add OWNERS file.

This package had no OWNERS, so changes could only be approved by global
approvers. This should instead be owned by the web team.

Change-Id: I3580b26e01d45e5225fef6d78f058cbce8663d8a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/427601
Commit-Queue: Mayank Patke <[email protected]>
Commit-Queue: Sigmund Cherem <[email protected]>
Reviewed-by: Sigmund Cherem <[email protected]>
Auto-Submit: Mayank Patke <[email protected]>

Author: fishythefish

pkg/node_preamble/OWNERS

@@ -0,0 +1 @@
+file:/tools/OWNERS_WEB