fix: Enable transit mode encryption var as it is now available in redis

[willejs]

Description

This allows you to set transit mode encryption for instances other than memcached, but retains the existing behavior of setting it to true for memcached by default.

Motivation and Context

I want to beable to set this for redis, which i currently cannot. If you cant set this, you can't create users, so you need to be able to set this.

Breaking Changes

None, see comment and above.

How Has This Been Tested?

• I have updated at least one of the examples/* to demonstrate and validate my change(s)
• I have tested and validated these changes using one or more of the provided examples/* projects

• I have executed pre-commit run -a on my pull request

[bryantbiggs]

if support was added for this, we'll need to ensure the min supported version of the AWS provider supports this as well

[willejs]

Good point, I tested this locally and It looks like this was added back in https://github.com/hashicorp/terraform-provider-aws/releases/tag/v5.16.0 so it should be fine?