Obtain EKS token via SDK

### Describe the feature

The EKSClient currently does not offer an `getToken()` method.
The STSClient also does not offer a method to presign a url.

### Use Case

We try to access an eks kubernetes cluster from a lambda.
Ideally, I should add the lambda's role to the clusters `aws-auth` configmap and use the EKSClient to generate a token, just like I would be able to do on the cli.

On the CLI I can do `aws eks get-token --cluster-name test` to get a token. There is to my knowledge no way to do this via the sdk for php.

### Proposed Solution

Implement the `getToken()` method for the EKSClient.

### Other Information

_No response_

### Acknowledgements

- [ ] I may be able to implement this feature request
- [ ] This feature might incur a breaking change

### SDK version used

3.249.0

### Environment details (Version of PHP (`php -v`)? OS name and version, etc.)

PHP 8.1.13 (cli)