Implement Colbert for Optimum

[wwymak]

Feature request

Add logic for colbert in the optimum engine so it returns token embeddings

Motivation

Since this is already supported for the torch engine, it will be useful to be able to use onnx versions of Colbert style models correctly as well

Your contribution

I can potentially submit a PR

(This issue is converted from https://github.com/michaelfeil/infinity/issues/512)