[QUA] Remove proposal check for dropdown and add hook to form

We discussed that checking the user proposal here doesn't really makes sense. I it would be a better practice to get the user proposal from the hook directly in the form component that uses it as a default value and let the submit validation do it's thing (and per form, we decide when we want to let the user change its value or not).

_Originally posted by @brnovasco in https://github.com/cnpem/sophys-web/pull/74#discussion_r3016179134_

Start by locating the dropdown component, its proposal check, and the form component that uses it as a default value. Trace how the user proposal is currently obtained and validated; the work is done when the form gets it through a hook and submit validation remains responsible for acceptance.

Written by the indexing model from the issue text.