Provide more clarity about which level of text representation is used

[roedoejet]

We should add a way for users to set the target_text_representation_level from inside the wizard, and also indicate how to change it in the main documentation guide since it is not intuitive to set it otherwise. In this wizard, this (and other model-specific questions) should take place after the dataset loop so that we can determine whether there is an option (e.g. all datasets need to have phones available if we want to set target_text_representation_level to phones).

[roedoejet]

We should add information about the g2p model that is applied here