m/n/core: implement GetClusterInfo

This implements Management.GetClusterInfo which is used to retrieve a
ClusterDirectory. This in turn will be used by nodes that wish to
register into a cluster.

This could've been skipped and instead Curator.Watch could've been used.
However, the Curator service is only really (currently) intended to be
used by node-to-node communications. To keep with the current design, we
implement a separate RPC, but we should maybe reconsider if this
separation makes sense.

Change-Id: Ie9d475731f4faafdc51a2aa51a1582ee1a259fd2
Reviewed-on: https://review.monogon.dev/c/monogon/+/340
Reviewed-by: Lorenz Brun <lorenz@monogon.tech>
diff --git a/metropolis/proto/common/common.proto b/metropolis/proto/common/common.proto
index 5a49520..63e6cfb 100644
--- a/metropolis/proto/common/common.proto
+++ b/metropolis/proto/common/common.proto
@@ -127,11 +127,7 @@
         message Address {
             string host = 1;
         };
-        repeated Address addesses = 2;
+        repeated Address addresses = 2;
     };
     repeated Node nodes = 1;
 }
-
-message ClusterIdentity {
-    bytes ca_fingerprint = 1;
-}