[Fargate] [request]: Run a Fargate task without requiring a Cluster or VPC

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**Tell us about your request**
As a user I'd like to have a way to run a Fargate task or service without the need to have a VPC and ECS cluster, much like the way it works with Lambda.

**Which service(s) is this request for?**
Fargate

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**

When running the task it's needlessly complex by the fact that I need to specify a VPC where the tasks would run, as well as a cluster. In many cases I'm fine with running the task anywhere.

As the author of a tool I'm shipping to users, configuring the VPC and ECS cluster without using infrastructure code adds friction for the installation of my app.

**Are you currently working around this issue?**
In another of my tools I create an ECS cluster and VPC as part of my app's deployment code, which then also needs subnets, routing tables, etc. All this required significant additional engineering effort. This second app I'm working on is supposed to be a simple CLI, which shouldn't require infrastructure code for creating such infrastructure bits.

**Additional context**
None

**Attachments**
If you think you might have additional information that you'd like to include via an attachment, please do - we'll take a look. (Remember to remove any personally-identifiable information.)

No repository file, test, or entry point is identified in the request. Start by reviewing the Fargate and ECS service interfaces involved, then define the required behavior and validation for running a task without an explicit VPC or cluster; done means the requested deployment path is supported and documented.

Written by the indexing model from the issue text.