feat: auto reply to public questions via dm 🤖

[ramiAbdou]

Description ✏️

Adds support for auto replying to questions asked in certain public channels. These responses are full LLM (RAG implementation) responses but are sent to DM. The key UX decision here is we don't want to take away from the community feel by having the bot reply publicly to every single message in a channel (despite that others may learn from it).

This PR:

• Implements the core answerPublicQuestionInPrivate function, which is similar to answerChatbotQuestion with a slightly different UX (ie: won't respond if nothing high confidence is found).
• Adds a slack.question.answer.private Bull job.
• Stores the "auto reply channels" in Redis, and reads that after a message is created in order to determine
• Adds a Public Question Answered Mixpanel event.
• Makes the user optional on a Mixpanel event, this is important for tracking non-user specific events such as our system automatically responding to public questions.
• Returns the ts of a Slack message when a notification is sent.
• Updates getAnswerFromSlackHistory to take in threads in order to be able to allow the caller to customize which threads the LLM takes into account and also adds thread references in that function.

Type of Change 🐞

• Feature - A non-breaking change which adds functionality.
• Fix - A non-breaking change which fixes an issue.
• Refactor - A change that neither fixes a bug nor adds a feature.
• Documentation - A change only to in-code or markdown documentation.
• Tests - A change that adds missing unit/integration tests.
• Chore - A change that is likely none of the above.

Checklist ✅

• I have done a self-review of my code.
• I have manually tested my code (if applicable).
• I have added/updated any relevant documentation (if applicable).