EKS [request]: Productize install-worker script

**Tell us about your request**
Productize the [install_worker.sh](https://github.com/awslabs/amazon-eks-ami/blob/master/install-worker.sh) script. Instead of just providing an AMI used for worker nodes, provide a package that can be installed during a build of an AMI to make it a worker node.

**Which service(s) is this request for?**
EKS

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
Due to compliance and specific packages we want to have baked into our AMI we cannot run the AMI produced by https://github.com/awslabs/amazon-eks-ami. While I cannot speak for all EKS customers, I have seen issues that suggest we are not the only ones. This makes upgrading to a newer EKS version difficult because this script can have breaking changes or add the [deletion essential files](https://github.com/awslabs/amazon-eks-ami/commit/9578a4519d224d65be953ef29cb45b30f746eb61) that may be used later on in our build.

**Are you currently working around this issue?**
Currently we have to evaluate each change between releases to ensure nothing has been added that will drastically effect our product. While this seems reasonable for all third product dependencies, if this particular script was treated as an artifact perhaps less breaking changes would be introduced.

**Additional context**
I see this as a yum package that can be installed during a packer build that simply runs this script with small guarantees with sane defaults for maximum user consumption.

Start by reading install-worker.sh in the amazon-eks-ami repository and compare how it is used when producing the current worker-node AMI. Review the requested yum package and Packer-build context, then define the package's guarantees and sane defaults. Done means the worker setup can be installed during an AMI build without requiring the published AMI.

Written by the indexing model from the issue text.