Create and register a task. Returns the task object.

• name is a unique task name.
• prereqs is an array of prerequisite task names. Prerequisites can be normal task names, file task names, file paths or globs (wildcards).
• action is an optional function that is run if the task is selected for execution (type Action = (this: Task) => any;).
• To fetch an existing task omit both the prereqs and action parameters.