OWNERS: Add new roller SA

Bug: b/240166082
Change-Id: Ibad5caef7b87bf81afd51b49e5c788e4c8ca91fa
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/150913
Presubmit-Verified: CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Erik Gilling <konkers@google.com>
Pigweed-Auto-Submit: Rob Mohr <mohrr@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/OWNERS b/third_party/OWNERS
new file mode 100644
index 0000000..3a75bf0
--- /dev/null
+++ b/third_party/OWNERS
@@ -0,0 +1 @@
+pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com