add sig node approver

Signed-off-by: Rita Zhang <rita.z.zhang@gmail.com>

Author: ritazh

keps/sig-auth/5018-dra-adminaccess/kep.yaml

@@ -11,7 +11,7 @@ reviewers:
   - "@enj"
 approvers:
   - "@enj"
-  -  # SIG-Node
+  - "@mrunalp"
 
 see-also:
   - "/keps/sig-node/4381-dra-structured-parameters"