m/n/c/curator: implement Management.ApproveNode

This takes a node from NEW to STANDBY. This is the second-to-last
step requires in a node's regsitration flow.

Change-Id: I88f9c7d2cd824c7d3182195b784a725ec9528d28
Reviewed-on: https://review.monogon.dev/c/monogon/+/442
Reviewed-by: Mateusz Zalega <mateusz@monogon.tech>
diff --git a/metropolis/proto/ext/authorization.proto b/metropolis/proto/ext/authorization.proto
index 42beb88..60ad68a 100644
--- a/metropolis/proto/ext/authorization.proto
+++ b/metropolis/proto/ext/authorization.proto
@@ -22,6 +22,7 @@
     PERMISSION_GET_REGISTER_TICKET = 1;
     PERMISSION_READ_CLUSTER_STATUS = 2;
     PERMISSION_UPDATE_NODE_SELF = 3;
+    PERMISSION_APPROVE_NODE = 4;
 }
 
 // Authorization policy for an RPC method. This message/API does not have the