Update UI hint directive (#59)

Keeping parity with the implementation in Assistant NLP.

* Add in defaults for ui-hint directives

* Correct the `text` key for both UIHint and AsrHint

* Remove unused/unsupported `display_immediately`

* Fix typing

* Update tests

* Use `prompt` only when provided

* Update poetry.lock and pyproject.toml file

Author: Christian Mata