feat: Add create_autoscaling_group option and extra outputs

[sethpollack]

Description

adds create_autoscaling_group to self-managed-node-groups and adds image_id and user_data outputs.

Motivation and Context

Currently to use this module with something like karpenter or spotinst you need to create a nodegroup and scale it down in order to have the iam role, userdata, etc. created for you.

You can then do something like this to get all the data you need:

data "aws_autoscaling_group" "spotinst" {
  name = module.eks.self_managed_node_groups["spotinst"].autoscaling_group_name
}

data "aws_launch_configuration" "spotinst" {
  name = data.aws_autoscaling_group.spotinst.launch_configuration
}

iam_instance_profile  = data.aws_launch_configuration.spotinst.iam_instance_profile
security_groups       = data.aws_launch_configuration.spotinst.security_groups
image_id              = data.aws_launch_configuration.spotinst.image_id
user_data             = data.aws_launch_configuration.spotinst.user_data

This PR eliminates the extra hoops by adding the create_autoscaling_group option and exporting the image_id and user_data.

[bryantbiggs]

Thanks for the PR @sethpollack - I think the addition of create_autoscaling_group is great and can see its use case. However, since this project does not use launch configuration and only supports launch template, do we still need to export ami_id and user_data? This is all typically handled in the exported launch template which I know Karpenter uses, I haven't worked with Spotinst though

[bryantbiggs]

Lets also add this create_autoscaling_group variable to the root node_groups.tf please

Missed this - already there, thanks!

[sethpollack]

@bryantbiggs No spotinst doesn't use a launch template, you need to provide those values: https://registry.terraform.io/providers/spotinst/spotinst/latest/docs/resources/ocean_aws

[bryantbiggs]

Thank you for the PR!

[antonbabenko]

This PR is included in version 18.21.0 🎉

[sethpollack]

Thanks!

[github-actions]

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