fix: Case insensitive matching deprecated

[mengesb]

Description

Motivation and Context

Case insensitive matching has been deprecated on elasticache_user resource

Breaking Changes

This should not be a breaking change

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

[mengesb]

The default use of the user-group module results in an engine value of REDIS, this should now be redis per the following error message:

Warning: Case Insensitive Matching Deprecated
with module.elasticache_user_group.aws_elasticache_user.default[0]
on .terraform/modules/elasticache_user_group/modules/user-group/main.tf line 36, in resource "aws_elasticache_user" "default":
  engine               = try(var.default_user.engine, "REDIS")
Expected an exact match to "redis", got "REDIS". Case insensitive matching is deprecated for this argument. Update the value to an exact match to suppress this warning and avoid breaking changes in a future major version.

[mengesb]

As a work around, if in the default_user {} or user {} blocks, the user can specify the engine parameter and assign redis to bypass it, however the default module behavior produces this behavior without this fix