Speed up building Bottlerocket image in AWS CodeBuild

When I first moved building Bottlerocket AMI from an EC2 host to AWS CodeBuild, I was hit by a very slow build. On an EC2 instance, I built both the x86 and Arm versions on x86 instances, and fresh builds finished in 5 minutes. However, on CodeBuild with more vCPU and memory, the build process was painfully slower. The x86 CodeBuild uses a compute of "145 GB memory, 72 vCPUs". The build finishes…