feat(chat): add parent_id to messages for tree navigation

[danyalxahid-askui]

• Introduced parent_id field in Message models to establish parent-child relationships between messages.
• Updated ChatHistoryManager, MessageService, and related components to support tree navigation based on parent_id.
• Enhanced message listing functionality to allow retrieval of messages in a tree path.
• Added migration script to update existing messages with appropriate parent_id values.
• Updated relevant tests and documentation to reflect these changes.