aws providers: minimal policy documents

For the following providers, we should document/provide the minimal set of policies that allows it to function. For example, the first thing that happens in the EKS provider is:

```
Error: getting availability zones: getting availability zones for us-west-2:
UnauthorizedOperation: You are not authorized to perform this operation.
```

- EKS Provider
- EC2 Provider
- Sonobuoy Provider (when used with an EKS cluster)

Start by reviewing how the EKS, EC2, and Sonobuoy providers access AWS, beginning with the EKS availability-zones failure described in the issue. Document or provide the minimal policies required for each listed provider, including Sonobuoy when used with an EKS cluster.

Written by the indexing model from the issue text.