[Feature Request] Support pointer-generator networks on T5 BeamSearch

### Describe the feature request

Support Pointer generator network ([Get To The Point: Summarization with Pointer-Generator Networks](https://arxiv.org/pdf/1704.04368)) in T5 models

### Describe scenario use case

We have note generation models for different application, and we are currently running those using a fork of onnxruntime. We would like to contribute this back on the mainline.

#### Subtasks
- [x] #23123
- [x] #23124

Start by reviewing the T5 BeamSearch implementation and the completed subtasks #23123 and #23124. Done means pointer-generator network support is available for T5 models, but the issue does not name specific files or tests.

Written by the indexing model from the issue text.