Retrofit solution to support "one-click command" SSH

[gwright99]

As per AWS blog https://aws.amazon.com/blogs/compute/secure-connectivity-from-public-to-private-introducing-ec2-instance-connect-endpoint-june-13-2023/, "One click command" section.

Example: aws ec2-instance-connect ssh --instance-id i-0aa722a7cce6f98xx

Considerations

• If EC2 instance and AWS Batch instances are in same subnet, access can be streamlined (i.e. no need to configure ssh_config and retain local copy of pem file).
• If Batch instances live in different subnets, I believe an SSH key still needs to be declared/used. In such cases, it might make more sense to still generate the artefacts (to allow an ssh-forwarding jump).
• Supporting two authentication methods will require additional conditional logic to be added to the file-copying logic (i.e. right now it is 100% ssh whereas introducing this modification would mean some installations use ssh while others use aw ec2-instance-connect ssh; I'm not sure what this change would have on scp commands).

Impacts

• If decision is made to implement, IAM permissions will need to be modified to allow TF to access the EC2 to copy file and execute Ansible playbooks.

Initial Inclination

I'm inclined to continue generating extra artefacts and keep the Bash logic simple (_i.e. 100% ssh / scp). Opening this ticket so other users of the tool can chime in.