Add copilot chat plugin to leverage AI to answer user queries based on questions and answers

## Is your feature request related to a problem? Please describe

It's actually a proposal. I think it's very suitable to add AI ability to Apache Answer cause it's an QnA platform. I think we can implement it as a plugin but I'd like to put issue here for more audience. I've already done some POC, feel free to check below demo. Welcome any comments and discussions.

https://github.com/user-attachments/assets/28a848f2-77ee-4dec-9ed3-9dd06c65f21e

## Describe the solution you'd like

As showed in above demo.

There're also some changes needed in answer repo, e.g.
1. supporting some plugin configs depend on others, and only show when it's a specific value.
2. it could be a new plugin type, cause it needs pass the `syncer` and add some REST API for chats.

If it's accepted, I can also implement these as well as this plugin itself.

Inizia esaminando il sistema di plugin di Apache Answer, la gestione della configurazione, l'integrazione del syncer e l'architettura della REST API. Lo stato finale proposto includerebbe un plugin di chat Copilot accettato, oltre al supporto per la configurazione dei plugin dipendenti e delle API di chat, ma l'issue non identifica file, test o un ambito di implementazione definito.

Scritto dal modello di indicizzazione a partire dal testo della issue.