Automatic rollback variable change to a list of string type

### Describe the Feature

Describe Feature
When trying to select the type of automatic rollback by default it uses "DEPLOYMENT_FAILURE"

the suggested change is to change the value from string to list(string) to be able to use both options to cover those edge cases cover

### Expected Behavior

able to select both options for automatic rollback

### Use Case

cover edge cases in which applications are healthy but throwing multiples errors

### Describe Ideal Solution

```
variable "auto_rollback_configuration_events" {
type = list(string)
default = "DEPLOYMENT_FAILURE"
description = "The event type or types that trigger a rollback. Supported types are `DEPLOYMENT_FAILURE` and `DEPLOYMENT_STOP_ON_ALARM`."

}

dynamic "auto_rollback_configuration" {
for_each = local.auto_rollback_configuration_enabled ? [1] : [0]

content {
enabled = local.auto_rollback_configuration_enabled
events = var.auto_rollback_configuration_events
}
}
```
allowing use both options for automatic rollback

### Additional Context

I think will make more dynamic the use of the module to cover edge cases