(Fix) Json serialization in database migrations

[Roardom]

When the switch was made in the database migrations to use the query builder instead of eloquent models in e67f7dc, the json casting provided by the eloquent models weren't accounted for. We have to deserialize and serialize the json manually now.

[what-the-diff]

PR Summary

• Update to User Notifications Table
  This change offers a new function named $migrate which transforms input and output formats more efficiently. This function is now utilized within a loop in the code, making the processing of each 'field' smoother and more systematic.

• Enhancements in User Privacy Table
  Similarly, the User Privacy Table has also seen improvements. A similar $migrate function was introduced to streamline the input-output format conversion. This upgraded function is now used within a loop, thus making the handling of each 'field' more efficient and organized.