Address eksctl warning regarding custom AMIs

#### Description

When clustering up, the following warning is emitted:
```
Custom AMI detected for nodegroup cx-ws-cpu-large-2. Please refer to https://github.com/weaveworks/eksctl/issues/3563 for upcoming breaking changes
```

#### Context

It seems that this will be necessary starting in eksctl v0.52.

https://github.com/weaveworks/eksctl/issues/3563

https://eksctl.io/usage/custom-ami-support/