[ECS] [request]: Increase "Tasks in PROVISIONING state per cluster" service quota

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**Tell us about your request**
Currently, the 'Tasks in PROVISIONING state per cluster' limit is 300, as listed on https://docs.aws.amazon.com/AmazonECS/latest/userguide/service-quotas.html. (In 2020, this limit was 100, but it has since increased to 300. [source](https://aws.amazon.com/blogs/containers/deep-dive-on-amazon-ecs-cluster-auto-scaling/)) I'd like to see this limit increased to 1000+, or made configurable, so we can increase this service quota on an account by account basis.

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

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
We are using ECS to create an EC2-based compute fleet for massive machine learning jobs that require 500+ worker instances. As a result of this limit, we cannot scale up all of our workers at once (in our case, each ECS task corresponds to a single worker).

**Are you currently working around this issue?**
Yes, currently we have keep polling the number of active tasks, catch errors from exceeding the 'Tasks in PROVISIONING state per cluster' threshold, and retry.

Start by reviewing the AWS ECS service-quotas documentation linked in the issue and the described 300-task PROVISIONING limit. Confirm how quota increases or account-level configuration are requested and whether the reported 500+ worker scaling case is supported. Done means AWS provides the requested higher or configurable quota, with the issue updated to reflect the outcome.

Written by the indexing model from the issue text.