Automatically populate PropertySource with instance metadata when running within an EC2 environment.

[kennyk65]

On startup within an EC2 environment, populate a PropertySource containing EC2 instance metadata (https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-instance-metadata.html). Running outside of an EC2 environment should result in no properties being set. Feature should work on both IMDS v1 and v2. Should allow disabling with a property. Should work whenever instance metadata is available, i.e. EC2, Elastic Beanstalk, ECS, EKS, etc.