Amazon Q: add Chat memory

## Problem
Amazon Q in visual studio is suffering from Dementia Light a lot.
When chatting with Amazon Q, Amazon Q looses track of the chat history pretty often, and starts giving totally unrelated reply's and not remembering gist content which Amazon Q just read a few reply's back

Also when Visual Studio crashes, you loose the whole active chat history and it's not beeing reloaded

## Expected behavior

Fix that Amazone Q gets a long and big chat memory, where it can relate the future answers to / from.
Fix that Amazone Q saves history periodic so that the chat is restored after visual studio restarted.

The issue names Amazon Q chat in the Visual Studio Code extension but no files, tests, or entry points. Start by locating chat-history handling and restart persistence in the extension. Done means retaining relevant context and restoring periodically saved active chat history after a crash or restart, with tests for both behaviors.

Written by the indexing model from the issue text.