[terraform] upgrade backup prod to 0.5.1

Summary: Upgrade production backup image to version 0.5.1

Test Plan: Tested on staging. Task is healthy

Reviewers: varun, bartek

Reviewed By: varun, bartek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D13962

services/terraform/remote/service_backup.tf

@@ -1,5 +1,5 @@
 locals {
-  backup_service_image_tag      = local.is_staging ? "0.5.1" : "0.5.0"
+  backup_service_image_tag      = local.is_staging ? "0.5.1" : "0.5.1"
   backup_service_container_name = "backup-service-server"
   backup_service_server_image   = "commapp/backup-server:${local.backup_service_image_tag}"
   backup_service_domain_name    = "backup.${local.root_domain}"