Implement an option to prefer that existing value on a NoSpecimen is not replaced with value from JSON file if they are different.

[Nicklas Nordborg]

This option should be used for the PAD, Sample date+time and RNA later date+time when it has already been registered on a NoSpecimen item. In this scenario we trust the registered values more since they are from a referral form that has already been registered by us. The different values in the JSON should be logged as warnings.

Note! If the existing item is a Specimen the values from the JSON file should be used. This scenario is different since it will create a new Specimen item and no values will be overwritten.

[Nicklas Nordborg]

In 6975:

Fixes #1442: Implement an option to prefer that existing value on a NoSpecimen is not replaced with value from JSON file if they are different.