Use maxmemory-policy noeviction for Chat redis

This is the value that Sidekiq recommends to avoid any data being
dropped if memory is exceeded. Without this configuration option Sidekiq
complains:

```
WARNING: Your Redis instance will evict Sidekiq data under heavy load.
The 'noeviction' maxmemory policy is recommended (current policy: 'volatile-lru').
See: https://github.com/mperham/sidekiq/wiki/Using-Redis#memory
```

To resolve this I've created a parameter group so that we can set this
parameter. From googling I also understand that we need to change
cluster-enabled too and then every other parameter is the same as
default AWS - however I still need to confirm that.

terraform/deployments/chat/redis.tf

@@ -17,6 +17,25 @@ resource "aws_security_group" "chat_redis_cluster" {
   }
 }
 
+resource "aws_elasticache_parameter_group" "chat_redis_cluster" {
+  name   = local.chat_redis_name
+  family = "redis7.1"
+
+  parameter {
+    name  = "cluster-enabled"
+    value = "yes"
+  }
+
+  parameter {
+    name  = "maxmemory-policy"
+    value = "noeviction"
+  }
+
+  tags = {
+    Name = local.chat_redis_name
+  }
+}
+
 resource "aws_elasticache_replication_group" "chat_redis_cluster" {
   apply_immediately          = var.chat_redis_cluster_apply_immediately
   replication_group_id       = local.chat_redis_name
@@ -25,7 +44,7 @@ resource "aws_elasticache_replication_group" "chat_redis_cluster" {
   num_cache_clusters         = var.chat_redis_cluster_num_cache_clusters
   automatic_failover_enabled = var.chat_redis_cluster_automatic_failover_enabled
   multi_az_enabled           = var.chat_redis_cluster_multi_az_enabled
-  parameter_group_name       = "default.redis7"
+  parameter_group_name       = aws_elasticache_parameter_group.chat_redis_cluster.name
   engine_version             = "7.1"
   subnet_group_name          = aws_elasticache_subnet_group.chat_redis_cluster.name
   security_group_ids         = [aws_security_group.chat_redis_cluster.id]