docs(x/wasm): Complete module README with Messages, CLI, and REST API documentation

[VolodymyrBg]

This pull request enhances the x/wasm module documentation by completing previously empty or TODO sections:

1. Messages Section:

   • Added comprehensive documentation for all message types (MsgStoreCode, MsgInstantiateContract, MsgExecuteContract, MsgMigrateContract, MsgUpdateAdmin, MsgClearAdmin)
   • Included Go struct definitions with parameter descriptions

2. CLI Commands Section:

   • Replaced TODO placeholder with detailed examples for all common operations
   • Added examples for uploading, instantiating, executing, and querying contracts
   • Included commands for admin operations (migrations, admin changes)

3. REST API Section:

   • Documented all available REST endpoints organized by functionality
   • Added code management, contract management, and transaction endpoints
   • Included example request format with BaseReq structure

These changes make the documentation much more useful for developers integrating with the Wasm module and provide a complete reference for both CLI and API interactions.