Add the ability to specify a EFS volume to mount in CDK scripts

[thisisaaronland]

TBD: Does it need to be an EFS volume to play nicely with auto-scaling or can we also allow an EBS volume with a "buyer beware" sticker?

[micahwalter]

EFS is probably the best option here as it can attach to multiple EC2 instances at once. However, if you only ever plan to have a single EC2 instance with multiple tasks running on it, then EBS might work as well.

Here are the docs on EFS with the CDK - You will need to:

1. Create the file system
2. Set permissions
3. Set security group settings so the EC2 instance can connect to EFS from within its VPC
4. Mount the EFS to the EC2 instance(s)
5. Tell your Dockerfile where to find it?

I'm a little fuzzy on the last step... but I think that's all you'll need to do.