I've disabled the use of unsafe features (Jinja extensions, migrations, and tasks) by default and added a new CLI switch `--UNSAFE` which enables them. Templates that don't use unsafe features are unaffected by this change. But Copier will raise an error for templates that do use unsafe features unless the `--UNSAFE` flag is passed.
I've not added an interactive prompt that asks for consent for using unsafe features because I think it's not clear how to distinguish between interactive prompting and raising an error when `--UNSAFE` is not passed. For this, I think Copier would need a switch that clearly states whether interactive or non-interactive mode is desired. Currently, `--defaults` implies this for questions.
Fixes https://github.com/copier-org/copier/issues/1137
BREAKING CHANGE: Copier raises an error when a template uses unsafe features unless the `--UNSAFE` switch is passed
