Mark SpecItem as deleted

[lnrd96]

User story

1. As a user I don't want items to be actually deleted from the database.
2. I need them to still be existing in the back-end and to be visible in the fron-end and
3. So that deleted items are only marked as deleted / deprecated instead of being deleted.

Acceptance criteria

The marking of deleted item is reflected in the database table.
The ER-Diagram was updated.
The SpecItem is marked as deleted in the front-end

NOTE:

Start first by implementing the back-end part of this ticket.
On friday, we are going to make sure whether the functionality is really expected to be reflected in the front-end as well or not.
https://docs.google.com/document/d/1y1VdDOkj_gLkftg0uH9UBA54rtTJA35-kLW_yp6gGQQ/edit

Definition of done (DoD)

Feature has been fully implemented
No known errors
All acceptance criteria were met
Test passes
Peer code review passed