Add CODEOWNERS file

Adapter implementations are being moved into the repo we should mirror
the code ownership of those implementations. This patch adds a
CODEOWNERS file which matches the pre adapter move ownership to be used
as a baseline for future changes for each individual adapter.

Author: kbenzie

.github/CODEOWNERS

@@ -0,0 +1 @@
+*                               @oneapi-src/unified-runtime-maintain