[Feature Request] Chat history deletion

Before anyone says anything, I know you can delete the messages. I think a great feature to have would be to delete the instance of the chat in general. While anyone who has access to an unlocked device can open keybase (unless for desktop client where you can force logout), and see who you talked to and when even if the messages are deleted.

I think just being able to delete the chat, like swiping left with any normal Signal or iMessage conversation, would be a really awesome feature.

I think my previous feature request of having a mobile lock screen would serve a similar purpose.

No files, tests, or entry points are named. Start by locating the mobile chat conversation list and the existing message-deletion flow, then compare the requested whole-chat deletion with the related mobile lock-screen request; done means a chat instance and its visible history can be removed as described.

Written by the indexing model from the issue text.