Add EC2 keypair

[ergonlogic]

We can inject a public key into Linodes directly when launching the instance. However, for EC2, this needs to be handled separately. I should still be able to pull in the user's public key, and create a key[air based on that.
Once https://github.com/ergonlogic/ansible-role-admin-users runs, it should clean up the ones we inject during launch.