Add CODEOWNERS (#13759)

diff --git a/.github/CODEOWNERS b/.github/CODEOWNERS
new file mode 100644
index 0000000..665175d
--- /dev/null
+++ b/.github/CODEOWNERS
@@ -0,0 +1,3 @@
+# Notify all committers of DB migration changes, per SIP-59
+# https://github.com/apache/superset/issues/13351
+/superset/migrations/ @apache/superset-committers