[instrument] norules meta instruction

[regisoc]

Brief summary of changes

Port #8714 to 24.1.

Testing instructions (if applicable)

1. take one linst instrument.
2. add a .meta file and/or add one line inside it: norules{@}true.
3. go to the frontend > candidate list > choose a visit and timepoint with the corresponding instrument.
4. try entering/modifying a form value with an empty answer (e.g. a blank value in a dropdown).
5. This should save the form.
6. Remove the norules{@}true from the meta file.
7. try saving the form from the frontend again, it should make an error.

[driusan]

This is a new feature. Why would it go in 24.1?

[regisoc]

For HBCD, linked to the optional fields issue of REDCap DD.

[regisoc]

Will be put as an override in HBCD.