AWS: Allow to encrypt the root block device of ec2 instance created

⚠ ️NOTE THAT THIS FORK IS MAINTAINED FOR CRITICAL BUG FIXES AFFECTING RUNNING COSTS ONLY. NO OTHER CONTRIBUTIONS WILL BE ACCEPTED. ⚠️

Currently there is no practical to add encryption to an already unencrypted EBS root volume in AWS. Lots of organisations require EBS volumes to be encrypted. The only effective solution is to create the encrypted volume on instance creation. This merge request seeks to fix this by giving a option to enable ebs encryption to the amazonec2 driver. I know this doesn't isn't fixing running costs but in my case it is limiting adoption of auto scaling gitlab runners.