feat: add support for chat messages dataset

[dlmgary]

Description

This PR adds:

• Support for chat messages dataset.
• Jupyter notebook explaining how to use the ChatMessagesDataset object.
• Fixes deprecated pydantic functions (i.e., json, parse_raw)
• Sample ChatMessagesDataset file.
• Updates ChatMessage model to support other parameters available in the OpenAI Completions API.

Tests

• no new tests required
• new tests added
• existing tests adjusted

Documentation

• no documentation changes needed
• documentation added or edited
• example notebook added or updated

[rlundeen2]

Blocking on the re-design. It's great work but let's sync! The big ideas here

• Shift to memoryInterface for anything an operator/pyrit wants to keep track of
• chat_message_normalizer should be the "truth", but we should be able to convert to/from that other formats from there

[rlundeen2]

I may want us to update the documentation later; not because it's unclear, but because datasets workflows are different from most of pyrit. E.g. we generally don't want folks to store multi-turn conversations using this.