Model validators not running for settings page updates

[mantariksh]

To replicate on staging:

1. on staging, add a valid collaborator to a form
2. in the database, edit this collaborator’s to have a non-whitelisted domain (e.g. @nonsense.gov.sg)
3. try adding a form field. this should fail because we correctly run model validators when adding form fields.
4. try editing the settings page (e.g. toggle captcha). the update goes through because the model validators aren’t running.

[mantariksh]

This is because Mongoose only runs the validator for the specific path being updated when we call findByIdAndUpdate. To discuss whether this is expected behaviour or not.

[mantariksh]

This is expected behaviour. Closing in favour of #1814.