Add test to verify eos_token is working as expected

[gkumbhat]

Description

In this PR, we identified that the eos_token can be set to None if the model is not "caikit" format converted. This can cause some confusion. We need to better handle eos_token situation, and whether not set it in our modules and always fetch it from the tokenizer or if we do set it then set it consistently and add tests for it