Update the UI after uploading a video to an exercise

After uploading an image, the exercise data is refetched so that the changes are reflected in the UI. This is currently not the case for videos, so the user doesn't know if the upload succedded. We would need to add a new query similar to useAddExerciseImageQuery and useDeleteExerciseImageQuery

Hi, I'm Mochi from the discord group, you can assign this too me 🙂

it's yours :)