Make ECR permissions configurable

[Puja]

As for #364 we have ECR permission in our EC2 instance policy, however, there might be use cases, where only certain clusters should have access to ECR and others not. For this we need to make the addition of the ECR policy configurable.

ping @rossf7

[Ross Fairbanks]

Closing. We added the ECR permissions a long time ago and we've had no requirement to make them configurable.

This is not difficult to do but it's more configuration to manage. If we do it at the installation level it causes a difference in config between installs. Doing it at the cluster level means we'd need to add it to the API.

cc @xh3b4sd @puja108

Please reopen if you disagree.