feat: Add 'messaging' module to the application

[alatras]

This commit introduces the 'messaging' module to the Cosmos SDK-based application. The module includes the following features:

• Core functionality for message storage and retrieval.
• Handling of message sending with fee deduction and permission checks.
• Custom queries for fetching messages.

Key changes and additions:

• Added keeper.go which defines the Keeper for the messaging module, including methods for storing, sending, and querying messages.
• Implemented AppendMessage, SendMessage, and related helper functions for managing messages.
• Configured default fee for message sending (set to 1000 by default, with a TODO for configurability).
• Integrated logging for important operations and error handling.
• Added unit tests to cover core functionality and ensure robustness.
• Updated app.go to include necessary imports and module initialization.

Documentation:

• Provided inline comments and documentation for key functions and components in keeper.go.