What is the primary file used to add a new plugin to a Flutter project?

In a Flutter project, the primary file used to add a new plugin is 'pubspec.yaml.' This file is the configuration file for Dart packages and contains metadata about the project, including dependencies. When adding a new plugin, you specify its version and other details in the 'dependencies' section of 'pubspec.yaml.' Understanding how to manage dependencies in this file is crucial for integrating external packages and extending the functionality of a Flutter app.