Add custom IAM role for GKE firewall resources

[brettcurtis]

This pull request adds a custom IAM role for GKE firewall resources in the host project. This role allows a GKE cluster in a service project to create and manage the firewall resources in the host project. The role aligns with Google's role naming convention and includes the necessary permissions.

Fixes #159

[infracost]

Infracost report

💰 Monthly cost will not change

_{This comment will be updated when code changes.}