Remove requirement for default VPC and default subnets from aws.exfiltration.rds-share-snapshot. Add output indicating if an attack technique is slow.

[briandefiant]

What does this PR do?

• Bug fix
• Enhancement

Motivation

• Error running aws.exfiltration.rds-share-snapshot  #140
• Add warning when detonating a slow attack technique #141

Checklist

Behavior when detonating aws.exfiltration.rds-share-snapshot prior to this change (with no default VPC or default subnets configured):

2022/12/06 12:46:58 Checking your authentication against AWS
2022/12/06 12:46:59 Warming up aws.exfiltration.rds-share-snapshot
2022/12/06 12:46:59 Applying Terraform to spin up technique prerequisites
2022/12/06 12:47:03 unable to run terraform apply on prerequisite: unable to apply Terraform: exit status 1

Error: Error creating DB Instance: InvalidSubnet: No default subnet detected in VPC. Please contact AWS Support to recreate default Subnets.
        status code: 400, request id: ______

  with aws_db_instance.default,
  on main.tf line 31, in resource "aws_db_instance" "default":
  31: resource "aws_db_instance" "default" {

Behavior after (including note about slow attack technique):

2022/12/06 13:33:57 Checking your authentication against AWS
2022/12/06 13:33:58 Note: This is a slow attack technique, it might take a long time to detonate
2022/12/06 13:33:58 Warming up aws.exfiltration.rds-share-snapshot
2022/12/06 13:33:58 Applying Terraform to spin up technique prerequisites
2022/12/06 13:41:44 RDS Snapshot exfiltration of RDS Instance terraform-______ is ready
2022/12/06 13:41:44 Sharing RDS Snapshot exfiltration with an external AWS account

[christophetd]

Thanks a lot! This looks great. I'll quickly test it locally and merge it afterwards. Appreciate the contribution!