Add serverless memcached for Chat service

terraform/deployments/chat/serverless_memcache.tf

@@ -0,0 +1,40 @@
+locals {
+  chat_memcached_name = "chat-memcached"
+}
+
+resource "aws_security_group" "chat_memcached" {
+  name        = local.chat_memcached_name
+  vpc_id      = data.tfe_outputs.vpc.nonsensitive_values.id
+  description = "${local.chat_memcached_name} memcached instance"
+  tags = {
+    Name = local.chat_memcached_name
+  }
+}
+
+resource "aws_elasticache_serverless_cache" "chat_memcached" {
+  name                 = local.chat_memcached_name
+  engine               = "memcached"
+  major_engine_version = "1.6"
+  cache_usage_limits {
+    data_storage {
+      maximum = 10
+      unit    = "GB"
+    }
+    ecpu_per_second {
+      maximum = 4000
+    }
+  }
+  subnet_ids         = [local.elasticache_subnets]
+  security_group_ids = [aws_security_group.chat_memcached.id]
+  tags = {
+    Name = local.chat_memcached_name
+  }
+}
+
+resource "aws_route53_record" "chat_memcached" {
+  zone_id = local.internal_dns_zone_id
+  name    = local.chat_memcached_name
+  type    = "CNAME"
+  ttl     = 300
+  records = [for k, v in aws_elasticache_serverless_cache.chat_memcached.endpoint : v.address]
+}