Wait for AMI becomes available after AMI is copied.

By listing multiple regions in `Infra.toml`, I take advantage of pubsys copying images to destination regions from the source region. However, I found the AMI is still in "Pending" status after `cargo make ami` says the AMI is registered.

```plain
18:51:38 [INFO] Registered AMI 'xxxx-alpha-1' in us-east-1: ami-xxxxx
```

Right now, I have to manually call `aws ec2 wait image-available` until the AMI becomes available. It would be good if pubsys could handle the wait-for-ami-available for me. Or at least, support an option to wait.

FYI: It can take a while for an AMI to become available. I've seen unfortunate cases where it takes more than 10 minutes. That caused the "aws ec2 wait image-available" to timeout and I have to retry "aws ec2 wait".

Start with the AMI registration path invoked by `cargo make ami`, and inspect how multiple regions from `Infra.toml` are processed. Compare that flow with `aws ec2 wait image-available`; done should mean the requested wait is handled or an explicit wait option is supported without requiring manual retries.

Written by the indexing model from the issue text.