CE-2872: Fix deleting instances
- Doesn't need to modify the instance generate method, since it already checks (in case the gitProjecId is empty in the DB) if the generated name already exist on Git as a project. If it exits, it uses that gutProjectId; if not, it creates it
- Deleting IOC instance needed a small modification: if the gitProjectId parameter in the request was NULL value -> don't call the gitlab API
- Deleting IOC type endpoint doesn't need modification since it already checks if the gitProjectId in the DB is NULL value or not