admin: add host weight to cluster json response (#5216)

This adds the host's weight to the `/clusters?format=json` response.

Signed-off-by: Venil Noronha <veniln@vmware.com>

Mirrored from https://github.com/envoyproxy/envoy @ 9039f24198c35939af411c4102fe64b9aba7d6b1

envoy/admin/v2alpha/clusters.proto

@@ -58,6 +58,9 @@ message HostStatus {
   // success rate or the cluster did not have enough hosts to run through success rate outlier
   // ejection.
   envoy.type.Percent success_rate = 4;
+
+  // The host's weight. If not configured, the value defaults to 1.
+  uint32 weight = 5;
 }
 
 // Health status for a host.