[ECS] Support for FSx for Lustre in ECS on EC2 and Fargate

Similarly to our upcoming support for EFS, we are considering support for FSx for Lustre filesystems within an ECS task definition. A sample task definition may look like the following (subject to change as we work on the design):

```json
{
"family": "my-task-with-fsx",
"volumes": [
{
"name": "myFSxVolume",
"FSxLustreVolumeConfiguration": {
"filesystem": "fs-1234"
}
}
],
"containerDefinitions": [
{
"name": "container-using-fsx",
"mountPoints": [
{
"sourceVolume": "myFSxVolume",
"containerPath": "/mount/fsx",
"readOnly": true
}
]
}
]
}