find-plugin: Search and controlled installation of community plugins in DSH

`find-plugin` is a DSH plugin maintained by graceen2331-prog, designed to simplify the search, review, and secure installation process of community plugins. The plugin registers two tools, `find_plugin` and `install_plugin`, without relying on a database or a Web UI. `find_plugin` searches GitHub for repositories with the `topic:dsh-plugin` topic, performs static checks, risk disclosure, and filters invalid candidates, returning up to five secure options. `install_plugin` executes the installation by obtaining a fixed Commit SHA and re-verifying the Bundle, utilizing the DSH approval mechanism (which allows only one-time authorization) and the official plugin management system.