[ECS] [Feature]: Warmpool Fargate Tasks

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**Tell us about your request**
Allow Fargate tasks to have a warmpool of tasks available. This warmpool can be configured to allow the tasks to start faster than is currently possible.

A task in the warmpool would already have an ENI available and ready to be assigned to a new task. Once a task would be stopped, the ENI and other resources would be returned to the warm pool and a next task would be prepared.

**Which service(s) is this request for?**
This could be ECS Fargate

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
When a fargate task start, it need to do a number of this which takes time. one task for example is assigning an ENI to the task. This task start up can take minutes in some cases where the same task starting using EC2 LaunchType, will take a second or two.

When a warmpool of tasks exist, Fargate will be able to take a task from the warmpool, if any are available, and the task can be started in a much speedier manner than compared a cold start.

**Are you currently working around this issue?**
Only solution would be to not use Fargate but to make use of EC2 LaunchTypes.

**Additional context**
N/A

Start by reading the issue description and its existing discussion about ECS Fargate task startup latency and warm pools. The payload names no repository files, tests, or entry points; done would require defining and implementing the requested configurable pool of prepared tasks and confirming faster task starts.

Written by the indexing model from the issue text.