Docs: Dependent validation (required/optional) of field based on other field

[pgangwani]

Is your feature request related to a problem? Please describe.
I am finding some what difficult to clearly use updateField for the form-atom where we need to omit a field which is not showing in render. this is due to other field selected, which makes this field not to be sent.

Describe the solution you'd like
I would like to get updateField example for below usecases:

1. Updating validation function whether it is required or not
2. In case hiding the field based on some other field, optional to be added and field should be cleared.

Describe alternatives you've considered
I am using derived atom based on multiple atom to recreate form atom but based on selection I cannot call derived atom.

Additional context
Add any other context or screenshots about the feature request here.