Add describe endpoint features

[MathiasVDA]

A couple of default queries such as listing a count of classes and predicates, .. to better understand an endpoint and help to write queries

Should open in a smart side panel or overlay. Something that can be made sticky but moved out of the way while query writing.

Results should be remembered even when new queries are executed.

[MathiasVDA]

1. Endpoint & Dataset Overview

• List all named graphs and their sizes to see how data is partitioned.
• Count total triples and triples per graph for a quick sense of scale.
• Find the most frequent namespaces to understand which vocabularies are in use.
• Check for custom functions or extensions exposed by the engine.

2. Vocabulary & Schema Discovery

• List all classes with instance counts to see the main entity types.
• List all properties with usage counts to learn the data’s “shape.”
• Extract SKOS concept schemes and counts of concepts per scheme.
• Identify shapes/constraints (SHACL/Shex) if present in the endpoint.

3. Instance-Level Exploration

• Sample instances per major class (top N per class) to inspect real records.
• List the most connected nodes (highest degree) to find hubs.

4. Labels, Languages & Literals

• Count labels/titles by language to see localization coverage.
• List properties that carry language-tagged literals (and their language distribution).

5. Interlinking & External Links

• List external namespaces referenced (e.g., Wikidata, GeoNames, DBpedia).
• Find entities with outbound links

6. Time & Geo Dimensions

• List temporal properties (creation dates, event times, validity intervals).
• List geospatial properties (WKT, lat/long) and CRS usage.
• Get a bounding box / centroid of all geospatial entities.