OPRUN-2913: Add DOWNSTREAM_OWNERS

Copy `OWNERS` to `DOWNSTREAM_OWNERS` to ignore upstream `OWNERS` files.

This will make figure downstream syncs easier (no need to ignore/modify
upstream OWNERS files).

Signed-off-by: Todd Short <[email protected]>

Author: tmshort

DOWNSTREAM_OWNERS

@@ -0,0 +1,21 @@
+approvers:
+  - dinhxuanvu
+  - kevinrizza
+  - anik120
+  - awgreene
+  - ankitathomas
+  - joelanford
+  - perdasilva
+  - oceanc80
+  - grokspawn
+reviewers:
+  - dinhxuanvu
+  - kevinrizza
+  - anik120
+  - awgreene
+  - ankitathomas
+  - joelanford
+  - perdasilva
+  - oceanc80
+  - grokspawn
+component: "OLM"