Feature/igw attachment

[caiovfernandes]

Add the attachInternetGateway boolean variable to attach or not a Internet Gateway within a public subnet.

• [x] Bugfix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [x] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [x] Documentation Update (if none of the other choices apply)
• [x] I have read the CONTRIBUTING.md doc.
• [x] I have added necessary documentation (if appropriate).
• [x] Any dependent changes have been merged and published in downstream modules.