feat: Remove launch configuration support, add support for ignoring desired_capacity

UPGRADE-5.0.md

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+# Upgrade from v4.x to v5.x
+
+If you have any questions regarding this upgrade process, please consult the [`examples`](https://github.com/terraform-aws-modules/terraform-aws-autoscaling/tree/master/examples/complete) directory:
+
+⚠️ Instructions detailed here are for migrating from `v4.x` to `v5.x`. For instructions on upgrading to `v4.x` first, please see [UPGRADE-4.0.md](https://github.com/terraform-aws-modules/terraform-aws-autoscaling/blob/master/UPGRADE-4.0.md).
+
+If you find a bug, please open an issue with supporting configuration to reproduce.
+
+## List of backwards incompatible changes
+
+- Launch configuration support has been removed. [AWS has stated that launch configurations will no longer receive updates](https://aws.amazon.com/blogs/compute/amazon-ec2-auto-scaling-will-no-longer-add-support-for-new-ec2-features-to-launch-configurations/) and that launch templates should be used since they are the successor.
+
+## Additional changes
+
+### Added
+
+- A second autoscaling group `idc` (ignore desired capacity) has been added to allow users to utilize an autoscaling group that will ignore changes to `desired_capacity`
+
+### Modified
+
+- `var.tags` was previously a list of maps of `key`, `value`, and `propagate_at_launch`. It has been changed to a standard map of `key` = `value` pairs
+- The use of `for_each = lookup(map.value, "attr", null) != null ? [map.value.attr] : []` pattern has been replaced with a more concise, readable pattern of `for_each = can(map.value.attr) ? [map.value.attr] : []`. This is a no-op change for users
+
+### Variable and output changes
+
+1. Removed variables:
+
+    - `propagate_name`
+    - `tags_as_map` (use `tags` instead)
+    - `use_lt` -> this is now the default; only launch templates are supported
+    - `launch_configuration`
+    - `create_lc`
+    - `use_lc`
+    - `lc_name`
+    - `lc_use_name_prefix`
+    - `user_data`
+    - `associate_public_ip_address`
+    - `spot_price`
+    - `placement_tenancy`
+    - `ebs_block_device`
+    - `ephemeral_block_device`
+    - `root_block_device`
+
+2. Renamed variables:
+
+    - `create_asg` -> `create`
+    - `create_lt` -> `create_launch_template`
+    - `lt_name` -> `launch_template_name`
+    - `lt_use_name_prefix` -> `launch_template_use_name_prefix`
+    - `lt_version` -> `launch_template_version`
+
+3. Added variables:
+
+    - `ignore_desired_capacity_changes` -> to flip between using a standard autoscaling group that respects `desired_capacity` setting or one that ignores
+
+4. Removed outputs:
+
+    - `launch_configuration_id`
+    - `launch_configuration_arn`
+    - `launch_configuration_name`
+
+5. Renamed outputs:
+
+    - None
+
+6. Added outputs:
+
+    - None
+
+## Upgrade Migrations
+
+### Before 4.x Example
+
+```hcl
+module "asg" {
+  source  = "terraform-aws-modules/autoscaling/aws"
+  version = "~> 4.0"
+
+  # Autoscaling group
+  name = "example-asg"
+
+  min_size            = 0
+  max_size            = 1
+  desired_capacity    = 1
+  health_check_type   = "EC2"
+  vpc_zone_identifier = ["subnet-1235678", "subnet-87654321"]
+
+  # Launch template
+  lt_name                = "example-asg"
+  description            = "Launch template example"
+  update_default_version = true
+  use_lt                 = true
+  create_lt              = true
+
+  image_id      = "ami-ebd02392"
+  instance_type = "t3.micro"
+
+  tags_as_map = {
+    extra_tag1 = "extra_value1"
+    extra_tag2 = "extra_value2"
+  }
+}
+```
+
+### After 5.x Example
+
+```hcl
+module "asg" {
+  source  = "terraform-aws-modules/autoscaling/aws"
+  version = "~> 5.0"
+
+  # Autoscaling group
+  name = "example-asg"
+
+  min_size            = 0
+  max_size            = 1
+  desired_capacity    = 1
+  health_check_type   = "EC2"
+  vpc_zone_identifier = ["subnet-1235678", "subnet-87654321"]
+
+  # Launch template
+  launch_template_name        = "example-asg"
+  launch_template_description = "Launch template example"
+  update_default_version      = true
+
+  image_id      = "ami-ebd02392"
+  instance_type = "t3.micro"
+
+  tags = {
+    extra_tag1 = "extra_value1"
+    extra_tag2 = "extra_value2"
+  }
+}
+```
+
+### State Changes
+
+There are no required state changes to migrate from `v4.x` to `v5.x`. If you are using launch configuration support, you can continue to do so with the `v4.x` version pinned or evaluate switching to a new autoscaling group that is backed by launch templates.
+
+If you wish to opt into the new feature `ignore_desired_capacity_changes`, you can perform the following state mv commands on your group(s) if desired:
+
+ℹ️ Be sure to add the `ignore_desired_capacity_changes = true` to your configuration.
+
+```bash
+terraform state mv 'module.<xxx>.aws_autoscaling_group.this[0]' 'module.<xxx>.aws_autoscaling_group.idc[0]'
+```
+
+For example, if you previously had a configuration such as (truncated for brevity):
+
+```hcl
+module "example" {
+  source  = "terraform-aws-modules/autoscaling/aws"
+  version = "~> 4.x"
+
+  # <your configs>
+}
+```
+
+After updating the configuration to the latest `v5.x` changes:
+
+```hcl
+module "example" {
+  source  = "terraform-aws-modules/autoscaling/aws"
+  version = "~> 5.x"
+
+  # <your configs>
+
+  ignore_desired_capacity_changes = true
+}
+```
+
+The associated Terraform state move command would be:
+
+```bash
+terraform state mv 'module.example.aws_autoscaling_group.this[0]' 'module.example.aws_autoscaling_group.idc[0]'
+```