[terraform] bump prod backup service image to 0.4.3

Summary: staging has been on 0.4.3 for a week and we haven't observed any issues. bumping prod to the same version

Test Plan: terraform plan

Reviewers: bartek, kamil, ashoat

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D13562

services/terraform/remote/service_backup.tf

@@ -1,5 +1,5 @@
 locals {
-  backup_service_image_tag      = local.is_staging ? "0.4.3" : "0.4.1"
+  backup_service_image_tag      = local.is_staging ? "0.4.3" : "0.4.3"
   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}"