Add whatever fields we need to make the DB multi tenant.

[afederici75]

• [X] Add Owner fields to all entities so we know who made what
  • [X] R&D on how to do this:
    • [X] There's something in the EF Core docs about this
  • More to add: -[X] CreatedOn/UpdatedOn -[skipped] Vote (1 to 10 number) -[X] IsStarred (already done)