Move nav_goals_generator from strands_util

This is needed to fix https://github.com/strands-project/strands_hri/pull/79
@ferdianjovan, just to save @Jailander the work of refactoring it later, could you please change this line to somnething similar to [this](https://github.com/Jailander/strands_navigation/blob/hydro-devel/joy_map_saver/launch/joy_map_saver.launch#L12) before we merge this?