feat: custom NodeGroup names without environment prefix

[Arzianghanchi]

What

• Updated the environment variable assignment in the NodeGroups configuration to allow the use of a custom NAME.
• Ensures that if each.value.name is not empty, it is used; otherwise, defaults to var.environment.
• Provides a fallback mechanism using try() to prevent errors in case of misconfiguration.

Why

• Enables flexibility in naming NodeGroups without requiring the inclusion of a default environment name.
• Ensures proper handling of cases where each.value.name is empty, preventing unexpected behavior.
• Improves maintainability and clarity of the Terraform configuration.