forge._model.schema_id is bucket dependent

```
from kgforge.core import KnowledgeGraphForge
config = "https://raw.githubusercontent.com/BlueBrain/nexus-forge/master/examples/notebooks/use-cases/prod-forge-nexus.yml"
forge_1 = KnowledgeGraphForge(config, bucket="bbp/atlasdatasetrelease", token=TOKEN)
forge_1._model.schema_id("CellComposition")
'https://neuroshapes.org/dash/cellcomposition'
```
but
```
forge_2 = KnowledgeGraphForge(config, bucket="bbp/atlas", token=TOKEN)
forge_2._model.schema_id("CellComposition")
Traceback (most recent call last):
File "/gpfs/bbp.cscs.ch/home/lcristel/venv/lib/python3.9/site-packages/kgforge/specializations/models/rdf_model.py", line 105, in schema_id
shape_iri = self.service.types_to_shapes[type]
KeyError: 'CellComposition'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "", line 1, in
File "/gpfs/bbp.cscs.ch/home/lcristel/venv/lib/python3.9/site-packages/kgforge/specializations/models/rdf_model.py", line 108, in schema_id
raise ValueError("type not found")
ValueError: type not found
```