feat(aws-ecs): add ECS/Fargate QueueWorkerService constructs

[piradeepk]

Implement an ECS and Fargate Queue worker that creates an sqs queue and fixes Step Scaling implementation to add ScalingTargetId and default AdjustmentType

Fixes #2396

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Pull Request Checklist

• Testing
  • Unit test added (prefer not to modify an existing test, otherwise, it's probably a breaking change)
  • CLI change?: coordinate update of integration tests with team
  • cdk-init template change?: coordinated update of integration tests with team
• Docs
  • jsdocs: All public APIs documented
  • README: README and/or documentation topic updated
  • Design: For significant features, design document added to design folder
• Title and Description
  • Change type: title prefixed with fix, feat and module name in parens, which will appear in changelog
  • Title: use lower-case and doesn't end with a period
  • Breaking?: last paragraph: "BREAKING CHANGE: <describe what changed + link for details>"
  • Issues: Indicate issues fixed via: "Fixes #xxx" or "Closes #xxx"
• Sensitive Modules (requires 2 PR approvers)
  • IAM Policy Document (in @aws-cdk/aws-iam)
  • EC2 Security Groups and ACLs (in @aws-cdk/aws-ec2)
  • Grant APIs (only if not based on official documentation with a reference)

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license.

[piradeepk]

Addressed all PR comments, and updated revision.

[rix0rrr]

Really, split on comma? Doesn't seem idiomatic to have to pass "my,command,with,args".

Why not define command as command?: string[] and let the caller worry on how to make a list of strings?

[piradeepk]

This was previously discussed: #2363 (comment), and @clareliguori had mentioned that the console currently supports comma delimited strings as command inputs.

[rix0rrr]

Well, I have to disagree with Clare there, sorry.

If there is structure to be had, I'd rather maintain it. I feel like the console decision to split on commas is because a list of input boxes are a more unfriendly UI than a single input box (for copy/pasting etc). We have no such problem though, everything is text.

If a user REALLY REALLY wants to split a comma-separated string, they can type:

"my,command,with,args".split(",")

themselves.

IOW, string[] leaves all options open, whereas an implicitly ,-split string precludes using commas in the command, for example.

I'm going to have to insist you change this back.

[rix0rrr]

Modulo the type of command: string[] and the build failures, I feel comfortable merging this.

[piradeepk]

Update command to string[]. Rebasing again, to try to resolve these build issues.

[piradeepk]

Resolved build failures. @rix0rrr can you merge this in? I'll refactor this into the new module as a separate PR

Points addressed