Add chat-plugin

[vzhang03]

Wanted to submit this PR to get a review on what changes should be worked on next. The functionality is all working as intended and has gone through testing by fellow URSI team. This plugin contains functionality to customize a chat with an LLM supporting various strategies for controlling bot-prompting and user prompting. This plugin also collects user keystrokes and comprehensive data on the conversation and communication with the LLM.

Main thing to work on is documentation and specifically how to guide people to navigate the process of using the backend. This plugin is hard to work with for people without coding experience, but not sure how to remedy this issue.

A smaller issue is a code rewrite moving the fetching and calling into a separate class. This would make it more friendly for devs to work with. Haven't done because prioritized building out prompting features for the other group. Not sure if necessary or if should just comment on the associated methods.

Lastly, should figure out where to handle styling and if should move away from styles.css to another place as well as allow researcher to customize.