The name of the keys for the IRI should be "@id" instead of "path"

## Description of the issue

The IRI are not just a path but a proper identifier.
This should be indicated by `@id`

## Ideas of solution

Rename `path` to `@id`

## Workflow checklist
- [x] I am aware of the workflow in [CONTRIBUTING.md](https://github.com/OpenEnergyPlatform/oemetadata/blob/develop/CONTRIBUTING.md)
