[ADR] type hints

# Type Hints

- type hints for translatable strings
- `flask_babel:LazyString`
- `flask_babel:gettext` returns a already translated string. there is no type to check other then string which doesn't help in the translatable context

# examples
- in [Check](https://github.com/inveniosoftware/invenio-checks/blob/master/invenio_checks/base.py#L12) of in `invenio-checks` it would be nice to know if `id` is of type `Final[str]` [Final](https://docs.python.org/3/library/typing.html#typing.Final) and `title` are of type `LazyString`. that would people who are working on translations help to know if those strings have to be marked as to translatable strings