Add dates to conversations

[Josh-XT]

This pull request includes significant improvements to the agixt package, focusing on optimizing database queries, adding timestamp columns, and ensuring safe migrations. The most important changes include optimizing the retrieval of conversations, updating timestamps on interactions, and adding a migration script for SQLite databases.

Optimizations and new features:

• agixt/Conversations.py: Optimized the get_conversations and get_conversations_with_ids methods to use a single query with a join to retrieve only conversations with messages, and ordered the results by the updated_at timestamp.
• agixt/Conversations.py: Updated the log_interaction method to update the updated_at timestamp for conversations whenever an interaction is logged. [1] [2]

Database schema changes:

• agixt/DB.py: Added created_at and updated_at timestamp columns to the Conversation class.

Migration script:

• agixt/DB.py: Added a run_safe_migration function to safely add the new timestamp columns to the conversation table in SQLite databases, ensuring existing rows are updated with current timestamps.