Support tags for task definition and propagate them to ECS tasks

[mozamimy]

Motivation

Cost allocation tags feature of AWS is useful to understand cost condition. In general, also tags are useful for metadata of AWS resources.

ECS supports tagging for task definitions, tasks and services. Tags attached to task definition and service can be propagated to its related running tasks. cf. https://docs.aws.amazon.com/AmazonECS/latest/developerguide/ecs-using-tags.html

This patch adds a support tagging for task definitions and propagate these tags to tasks generated from that definition.

What not to do

This change doesn't support tagging for services and propagate tags only from task definitions (it means no service propagate tags).

This is for simplicity of implementation and specification of Hako. When we use Hako, 1 hako app has 1 service and 1 task definition basically. So it's enough define tags to a task definition and propagate them to running tasks generated from the definition. I think this is natural and it can cover general use-cases.

Hako config

{
  scheduler: {
    type: 'ecs',
    tags: {
      Project: 'awesome-project',
    },
  },
}

@eagletmt Please review 🙏

[eagletmt]

It looks reasonable to support propagate_tags=TASK_DEFINITION only 👍