Json/Migrations: flow the json type mapping (or relevant type mapping info) to column in the model differ so we can create correct default value and clr type for json column operation

[maumar]

For now the clr type (and default value) are hard-coded. It's not a major issue as we can't really do anything intelligent here, apart from creating a string representation for empty json (which won't work if the model requires an entity there), but it will be "more correct" way of doing things

[AndriySvyryd]

Needed for #28591