Mark Contracts as invalid if Contract Definition is deleted

[SebastianOpriel]

Feature

Description

The Core EDC has loose coupling of entities. For example, one can delete an asset for a live contract agreement and have future transfer processes fail.

This is an alternative solution to #462

Solution Proposal

Flow:

• Provider: Create Asset, Policy and Contract Definitions
• Consumer: Negotiate contract, successfully transfer data
• Provider: Delete Contract Definition
• Consumer: Previously agreed contract still visible [I expect, that this shall be marked somehow as "transfers no longer possible: stopped"
• Consumer: Error on data transfer
• Provider: No transfer history error [should be expected behavior, right?]
• Provider: Previously agreed contract still visible [I expect, that this shall be marked somehow as "transfers no longer possible: stopped"