[Story] Add draft semantic models for data exchange requests & approvals

[ReneSchroederLJ]

As PURIS developer,
I want standardized representation of new data models,
so that I can use them as reference for implementations.

Hints / Details

• draft models for DataExchangeRequest and DataExchangeApproval shall be provided
• the draft models shall be added to a drafts folder at the root of the repository
• each submodel shall be in its own folder
• for each submodel the .ttl file as well as an example json shall be provided

Outcome / Acceptance Criteria

Outcome

• the semantic models for each data model are available

Acceptance Criteria

Out of Scope

• other generated artifacts like html files are not included