[Feature] Allow for Persistent, User-Defined Starting Chat History

[knuurr]

Problem Description

In some scenarios it is useful to manually craft beginning chat history, to give model better idea of how to respond properly , i.e when achieving certain formatting or wording is critical.

This is not always possible to achieve using only crafted system prompt. Injecting custom, artifical history is sometimes (in my opinion often) quicker and more robust way to give model an idea of what "good" response is, or what a "bad" response might be.

Proposed Solution
Allow to define per-chat starting artificial chat history, which could also survive "Clear All Messages" purge. This is simmilar to how bundled example chats are shipped with Chatbox, but I also focus specifically on surviving any history clearing attempt (sometimes I need to clear chat history).

Additional Context
None.