eks variants: integrate ImagePullSecrets with Secrets Manager

[mchaker]

What I'd like:

In trying to enable a local caching registry, customers want to add imagePullSecrets to EKS node configurations.

Full context: #2351

Any alternatives you've considered:

n/a

[stmcginnis]

Concern appears to be the storage of the credentials in plaintext, so having them pushed into something like the secrets manager would give a little more safety. Seems like a good thing to improve, but we probably need a proposal of how to implement something like this. Putting in the icebox backlog until someone has time to investigate more.