(aws-eks): `AccessEntry` should support `IPrincipal` or `IGrantable`

### Describe the feature

The AccessEntry construct currently takes `string` for the `principal` prop. This is counterintuitive when compared with the rest of CDK where similar props take an `IPrincipal`/`IGrantable`. You should be able to pass a `Role` or `User` directly to `AccessEntry` without calling `.arn` yourself.

### Use Case

I want intent based syntax, especially when using it in the context of `cluster.grantAccess()`, where in most other places you would just pass the `IPrincipal`/`IGrantable`.

### Proposed Solution

I'd love it if this was implemented overriding the old prop as it's named best for it, but I get not wanting to break backwards compatibility. I'd suggest doing that for the `eks-v2-alpha` where you are explicitly breaking backwards compatibility. For the current stable version, perhaps you could add a new prop called `grantee` that takes an `IGrantable`.

### Other Information

I'm open to discussion on whether `IGrantable` or `IPrincipal` makes more sense.

### Acknowledgements

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

### CDK version used

2.187.0

### Environment details (OS name and version, etc.)

n/a

Start at the EKS AccessEntry construct and its principal prop, then compare the cluster.grantAccess() call path with existing IPrincipal/IGrantable usage. Done means allowing a Role or User directly while accounting for stable-version compatibility and the eks-v2-alpha proposal; validate the chosen API with the relevant construct tests.

Written by the indexing model from the issue text.