[REF] transform the setting of defaults in CustomField::create to be like (some)...

[REF] transform the setting of defaults in CustomField::create to be like (some) other entities

This patter (massaging the params & then copying) is more consistent. PR also moves creating the transaction to the start of the fn

I am cleaning up towards adding a bulk function that can be utilised by api v4 to create multiple fields with some efficiency on
sql statements (which matters when adding 2 or more fields to a large table)