Add possibility for adding several security groups

[Tomas Bäckman]

Describe the Feature

Currently there is no way to have several security groups on the created cluster.
I would like to be able to add extra security groups, not only as rules in the main security group but as separate rules.

Expected Behavior

The resource for security group can take a list, so the current only security group that is added to the cluster should bascially be made into a merged list of that and an input list variable with more ids).

So solution is an optional list variable with security groups, so that the resource can be setup/modified both with and without those extra groups.

Use Case

For example Glue requires that both the job and the database have the same security group (that have ALL traffic open attached to both). So more security groups need to be added. Now we have to add manually, and they get removed with each terraform apply and need to be readded, quite annoying..