[ECS] [request]: Support for FSx volumes in CloudFormation resource type AWS::ECS::TaskDefinition

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**Tell us about your request**
What do you want us to build?
CloudFormation resource type AWS::ECS::TaskDefinition doesn't have support for mounting FSx volumes.
The "Volumes" property supports "DockerVolumeConfiguration", "EFSVolumeConfiguration", "Host" and "Name", but it doesn't have properties that would support mounting an FSx volume to a task definition.

**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 simply trying to map a mountpoint in the ECS windows Cluster server to our FSx Share - but because the function is missing from cloudformation - we are having to invoke a workaround with a custom resource powered by a Lambda function - this adds delay to our launches.

**Are you currently working around this issue?**
As a workaround, we had to develop a Custom resource in CloudFormation, powered by a Lambda function, which creates a Task Definition upon stack creation/updates and it configures a Task Definition JSON file with the "mountPoints", "volumes" and "fsxWindowsFileServerVolumeConfiguration" properties, configured to support FSx.

**Additional context**
Given that FSx was announced in November, 2018 and FSx support for Windows ECS containers was announced in November 2020, we would expect that CloudFormation support for FSx mount points in ECS Task Definitions would be available almost 1 year later.

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