CIMNotebook: Support SPARQL Notebook Workspace/Local Endpoints in VSCode extension

[spah-soptim]

The VSCode extension SPARQL Notebook stores endpoints for the workspace.

We currently only support the in-line / cell-specific endpoint definition.

If possible, it would be cool to have support for the endpoint in the SPARQL Notebook:
https://github.com/zazuko/vscode-sparql-notebook#endpoints

So the extension uses those endpoints out of the box without requiring a separate endpoint config for CIMVocabCheck.