Add feature to display welcome message with regex

For any message such as `hello world!`, as long as it contains `hello world` should prompt the welcome message to be displayed

Start by locating the bot's welcome-message handling and the existing message-matching behavior. Confirm how messages such as `hello world!` are processed, then define completion as matching messages that contain `hello world` and displaying the welcome message without changing unrelated responses.

Written by the indexing model from the issue text.