Use AL2 build image instead of golang/debian

[mckern]

Remove the forced static compilation and use AL2 as a build environment, not just a runtime environment. This coincidentally also makes the lambda container smaller, so 🎉.

[mckern]

Our binaries work as expected:

$ docker run -it --rm --entrypoint=/bin/bash imager:b44b0697
bash-4.2# /kubeapply-lambda
FATA[0000] No github token or app key information provided
bash-4.2# kubeapply
kubeapply automates onebox workflows

Usage:
  kubeapply [command]

Available Commands:
  apply        apply runs kubectl apply over the resources associated with a cluster config
  check        check verifies that all dependencies are installed at their proper versions
  diff         diff shows the difference between the local configs and the API state
  expand       expand expands all configs associated with the cluster config
  help         Help about any command
  pull-request pull-request mimics the behavior of the webhook lambda (for testing only)
  validate     validate checks the cluster configs using kubeconform and (optionally) opa policies

Flags:
  -d, --debug     Enable debug logging
  -h, --help      help for kubeapply
  -v, --version   version for kubeapply

Use "kubeapply [command] --help" for more information about a command.
bash-4.2#