Use a new quick chat for each request

[aeschli]

Testing #6321

• select an issue and invoke 'Fix with Copilot'. Quick chat opens and proposes something
• select a different issue and invoke 'Fix with Copilot'. Quick chat adds that suggestion under the previous conversation.

As the two entries are not related to each other, I would prefer a new chat. With each request, the quick chat gets larger and difficult to navigate