Ensure AWS networking is mocked for (T)C2S airgap, add initial rke2 airgap deployment

Adds the following:

• private endpoints on intra (airgap) subnets for common aws services (s3, ec2, elb, asg, etc...) to mock (t)c2s as "airgapped network with aws services"
• very basic rke2 packer build that simply pre-downloads rke2 binary and boot images
• ci-airgap environment for rke2 airgap builds