feat: Add ASG lifecycle management Lambda function (#392)

This introduces an Auto Scaling Group instance termination lifecycle
hook using Lambda and related resources. The Lambda function is a Python
script that is triggered when the persistent runner instance in the ASG
is terminated. The function receives the instance ID of the "parent"
runner and queries for spawned instances that it launched to terminate.
Additionally, it will check for other "orphaned" instances that have a
`gitlab-runner-parent-id` tag that doesn't match an existing instance. This
resolves the issue where spawned instances could be orphaned when their
parent runner is terminated.

This feature is disabled by default.

The user data script is updated to provide the 'parent' instance ID as a
tag named 'gitlab-runner-parent-id' on spawned instances.

A new sub-module is provided called "terminate-workers". It is optional
to use this feature, and the input variable
`asg_terminate_lifecycle_hook_create` can be toggled `true` or `false`
for this behavior.

Author: npalm

README.md

@@ -6,6 +6,12 @@
 - [Prerequisites](#prerequisites)
 - [Usage](#usage)
 - [Examples](#examples)
+- [Requirements](#requirements)
+- [Providers](#providers)
+- [Modules](#modules)
+- [Resources](#resources)
+- [Inputs](#inputs)
+- [Outputs](#outputs)
 
 ## The module
 

modules/terminate-instances/main.tf

@@ -17,6 +17,7 @@ data "archive_file" "terminate_runner_instances_lambda" {
 }
 
 resource "aws_lambda_function" "terminate_runner_instances" {
+  architectures    = ["x86_64"]
   description      = "Lifecycle hook for terminating GitLab runner instances"
   filename         = data.archive_file.terminate_runner_instances_lambda.output_path
   source_code_hash = data.archive_file.terminate_runner_instances_lambda.output_base64sha256