refactor: added overlay base model for all overlay model to inherit.

[adekoder]

Description:

We are refactoring the naming of the respective models MaintainersEdit and PackageEdit and subsequent similar models to hand similar type of edit, they are basically an Overlay an not an Edit since we are not actually editing the maintainers or the packages.

This PR is to create a structure this type of models by introducing a Base Abstract Class that check similar model can inherit from, this keep the part of the system organise since there is already a pattern established here.

[fricklerhandwerk]

To avoid dumping dead code (however short-lived), I recommend doing the event name migration first (separately), and then moving the special cases under the base class together with the addition of the base class.

[adekoder]

To avoid dumping dead code (however short-lived), I recommend doing the event name migration first (separately), and then moving the special cases under the base class together with the addition of the base class.

sure ... noted

[fricklerhandwerk]

Depends on #944