feat: add plugin/read. (#14445)

return more information for a specific plugin.

codex-rs/app-server/tests/suite/v2/mod.rs

@@ -19,6 +19,7 @@ mod output_schema;
 mod plan_item;
 mod plugin_install;
 mod plugin_list;
+mod plugin_read;
 mod plugin_uninstall;
 mod rate_limits;
 mod realtime_conversation;