[terraform] bump prod tunnelbroker to 0.18-amqp

Summary:
Bartek implemented a fix for issues with tunnelbroker amqp in https://linear.app/comm/issue/ENG-9412/ecsstagingtaskstopalarm-triggered-for-tunnelbroker.

He also pushed an image with the fix that we'll be deploying later this evening

Test Plan: Will test with some iOS simulators on current staging environment that personal dms are working proper before landing

Reviewers: ashoat, varun

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D13599

services/terraform/remote/service_tunnelbroker.tf

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