Feature flag to allow turning on/off security group creation

[jdaws-bah]

Governance policies often times prevent the creation of Security Groups, so heavy modifications are needed to use the rke2-aws-tf repository in our environment. A feature flag is requested to turn on/off the creation of the Security Groups and pass our own pre-existing values. The implementation should mimic the IAM modules feature flag.

[jdaws-bah]

Additionally, we currently can't pass in target group arns to the agent-nodepool module, even though the nodepool module accepts a target_group_arns variable. I'd like to be able to pass target group arns if I so chose.

[aleiner]

Thanks for the feedback - a pending PR has been submitted, (#74), which will be reviewed as a potential fix for this issue.