changed field label in subject visit info https://git-r3lab.uni.lu/NCER-PD/scheduling-system/-/issues/331\#note_46155

added checks for forms
added check function in Study and StudySubject to avoid repeating a regex inline
removed previous checks in which the regex was rewritten
now the used regex is the one defined in the given study
added tests and migrations
changed functions in tests/functions to adapt the tests