[terraform] Deploy Tunnelbroker 0.18-amqp to staging

Summary:
Tunnelbroker image containing fixes from D13595.
Would be good to test them on staging.

Test Plan: terraform plan

Reviewers: ashoat, will, varun, kamil

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D13596

services/terraform/remote/service_tunnelbroker.tf

@@ -1,7 +1,7 @@
 locals {
   tunnelbroker_config = {
     docker_image = "commapp/tunnelbroker"
-    docker_tag   = local.is_staging ? "0.17" : "0.17"
+    docker_tag   = local.is_staging ? "0.18-amqp" : "0.17"
 
     grpc_port      = 50051
     websocket_port = 51001