dsh-sierra-leone: Sierra Leone Country Information Query Plugin

The DSH plugin `dsh-sierra-leone` is maintained by developer uckkk and is designed to provide agents with basic country data for Sierra Leone. Built with pure Node.js and requiring no network requests, the plugin includes built-in information across four dimensions: capital, population, currency, and continent. Users can easily install it with the `dsh plugin add` command and invoke the `country_info` tool. This plugin is suitable as a fast and reliable data source when developing agents that involve a Sierra Leone context.