Inconsistencies with _extends values

[Raphael-Gazzotti]

Paths should start with the “/” character or without. But we should not see both cases.

Non-exhaustive examples: (Sample of schemas in openMINDS_SANDS)

Sample of “schemas/atlas/atlasAnnotation.schema.tpl.json”

{ 

  "_type": "https://openminds.ebrains.eu/sands/AtlasAnnotation", 

  "_extends": "atlas/annotation.schema.tpl.json", 

... 

Sample of “schemas/atlas/brainAtlas.schema.tpl.json”

{ 

  "_type": "https://openminds.ebrains.eu/sands/BrainAtlas", 

  "_extends": "/core/schemas/products/researchProduct.schema.tpl.json",
...