feat: Add support for autoscaling group AMI override

[GaruGaru]

PR o'clock

Description

Resolves #1498
Allow users to specify different AMIs based on the instance type ( more details in #1498 )

Since aws has introduced eks support for arm instances the module should also support the creation of asg with mixed instance type (arm64, x64).

The suggested way to implement this feature is to create multiple launchtemplates and overriding the default launch template with a specific one related to the instance type.

Example

module "eks" {
  ...
  worker_groups_launch_template = [
    {
      name = "spot-1"
      override_instance_types = [
        "m5.large",
        "t4g.medium"
      ]
      override_instance_ami = {
        "t4g.medium" : "<custom_ami>"
      }
    },
  ]
}

This change introduce more complexity in the aws_launch_template creation since we now have to create multiple aws_launch_template for the same aws_autoscaling_group if override_instance_ami is specified.

In order to avoid the duplication of aws_launch_template.workers_launch_template the resource is not created using a for_each which creates a launch template for every node group * n. of specified overrides,
Ideas to reduce the complexity of the features are welcome.

Checklist

• README.md has been updated after any changes to variables and outputs. See https://github.com/terraform-aws-modules/terraform-aws-eks/#doc-generation

[AndriiBarabash]

Related PR - #1473

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