feat: Implement chat auto-reply feature

[rakshabesafe]

This commit introduces an auto-reply feature for chat messages.

New API Endpoints:

• POST /chat/autoreply: Allows you to set an auto-reply message for a specific phone number. The request body requires 'Phone' and 'Body'. It stores the rule per user.
• DELETE /chat/autoreply: Allows you to remove an auto-reply rule for a specific phone number. The request body requires 'Phone'.

Core Logic:

• Database: A new 'autoreplies' table is added via migrations to store user_id, phone_number, and reply_body.
• Message Handling: Incoming messages are checked against active auto-reply rules for the recipient user and the sender's phone number. If a rule matches, the predefined reply_body is sent back.
• Loop Prevention: Auto-replies are not sent to messages originating from the bot itself (IsFromMe check).

Documentation:

• API.md and the Swagger specification (static/api/spec.yml) have been updated to include the new endpoints, request/response formats, and error codes.