Ensure all data stored is encrypted in-transit for AWS Elasticache Replication Group

Data stored in the Elasticache Replication Group is not encrypted in-transit which could expose sensitive customer data.

In AWS Console -
To enable in-transit encryption when creating a replication group using the AWS Console, make the following selections:

1. Select redis as your engine.
2. Select version 3.2.6, 4.0.10 or later as your engine version.
3. Select Yes from the Encryption in-transit list.

In Terraform -

1. In the aws_elasticache_replication_group resource, set the transit_encryption_enabled field to true.

References:
https://docs.aws.amazon.com/AmazonElastiCache/latest/red-ug/in-transit-encryption.html
https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/elasticache_replication_group#transit_encryption_enabled