Users can create pitches for journalists

Trello: https://trello.com/c/0oul2GrI/44-users-create-pitches
Unused method argument - `batch_pitch_params`. If it's necessary, use `_` or `_batch_pitch_params` as an argument name to indicate that it won't be used. You can also write as `create_multiple_pitches(*)` if you want the method to accept any arguments but don't care about them.