policies generated by policy playground cannot be expanded

### Current Behavior
If I generate the simplest policy [in the playground](https://eclipse-tractusx.github.io/tutorial-resources/policy-playground/):

```json
{
"@context": [
"http://www.w3.org/ns/odrl.jsonld",
"https://w3id.org/tractusx/edc/v0.0.1",
{
"@vocab": "https://w3id.org/edc/v0.0.1/ns/"
}
],
"@type": "PolicyDefinition",
"@id": "{{POLICY_ID}}",
"policy": {
"@type": "Set",
"permission": [
{
"action": "use",
"constraint": [
{
"leftOperand": "BusinessPartnerNumber",
"operator": "eq",
"rightOperand": ""
}
]
}
]
}
}
```

and I try to expand it on the [JSON-LD Playground](https://json-ld.org/playground/)
I get this error:
```
jsonld.InvalidUrl: Dereferencing a URL did not result in a valid JSON-LD object. Possible causes are an inaccessible URL perhaps due to a same-origin policy (ensure the server uses CORS if you are using client-side JavaScript), too many redirects, a non-JSON response, or more than one HTTP Link Header was provided for a remote context.
```

### Expected Behavior
to being able to expand the policy correctly.
The policy actually works if ingested in the Tractus-X connector because the context it's cached there, but the `https://w3id.org/tractusx/edc/v0.0.1` url should point to the actual file uploaded somewhere to permit eventually other connectors or tools to being able to expand it correctly.