[QA] Improve Postman collection for M19 release

Scope

1. Validate the set of endpoints covered by the collection in terms of M19 release
2. Replace all opendes/osdu with their dynamic variables {{}}
3. Change links for the Datasets property on the real datasets Ids from the Configure Collection step
4. Create the v1/cleanup folder and move into all DELETE methods
5. Create the /cleanup folder for created records purge