This commit adds a new welcome.html file to display a message to the
user when no Git repository is open. The message informs the user that
DevChat is designed for answering questions about Git repositories and
asks them to open a Git repository folder to start using DevChat.
This commit adds a new webpack configuration for the webview part of the project. It includes the necessary rules for transpiling and bundling the TypeScript and React code, as well as the CSS and image files. The new configuration is added to the existing configuration for the extension. The devtool option is changed to 'source-map' for better debugging experience.
