fix: Use lowercase form of default engine "redis"

[armin-x86]

fix(user-group): use lowercase default for engine to prevent Terraform warning

Description

This PR updates the default value of the engine variable in the modules/user-group module from "REDIS" to "redis" to align with Terraform's expected values and eliminate deprecation warnings.

Background

Terraform has deprecated case-insensitive matching for the engine argument in the aws_elasticache_user_group resource. Using "REDIS" (uppercase) results in the following warning:

╷
│ Warning: Case Insensitive Matching Deprecated
│   on .terraform/modules/elasticache_user_group/modules/user-group/main.tf line 12, in resource "aws_elasticache_user_group" "this":
│   12:   engine        = var.engine
│
│ 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.
╵

Switching the default to "redis" ensures forward compatibility and removes the warning.

Changes

• Changed default = "REDIS" to default = "redis" in modules/user-group/variables.tf

References

• Terraform AWS Provider - aws_elasticache_user_group

Checklist

• Variable updated without breaking change
• Consistent with AWS provider requirements
• No documentation update necessary (default value only)
• Examples verified (N/A - not dependent on engine default)

---

Let me know if any additional context or changes are required.

[antonbabenko]

This PR is included in version 1.6.2 🎉

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