Refactor Default Values

[Hephi2]

Is your feature request related to a problem? Please describe.

Currently default values have two purposes:

1. When creating a new row, those values are prefilled in the corresponding column input fields
2. When a new column is created for a table that already contains some rows, the cells of the newly created column for those rows are filled with the default values. (More detailed: Whenever a cell value is null and has a default value, this value is shown in the table instead)

However, 2. is problematic since this creates problems with both frontend and backend filtering and more.

Describe the solution you'd like

Default values should only be used for the 1. purpose named above. For the 2. case you could add a new field to the create column modal that allows to fill the cell of this column for all existing rows with this value.

Describe alternatives you've considered

No response

Additional context

Related: #411