Fuseki UI: custom SPARQL query prefixes or examples

### Version

4.7.0

### Feature

The default SPARQL query

~~~sparql
PREFIX rdf:
PREFIX rdfs:
SELECT * WHERE {
?sub ?pred ?obj .
} LIMIT 10
~~~

Should be extendable with custom prefixes used in a database or graph. An optional set of sample queries would also help. Open question is where to store these configuration. Fuseki and database configurations beyond list of services are not made available other than via http://localhost:3030/$/datasets. An option would be to introduce a JSON configuration file in the webapp root at http://localhost:3030/config.json. This would allow for additional run-time configuration of the user interface (no need to rebuild) such as custom CSS, title, logo etc.

### Are you interested in contributing a solution yourself?

Yes

Start by inspecting the Fuseki UI's default SPARQL query and the dataset information exposed at /$/datasets. Define how optional prefixes, sample queries, and runtime UI settings would be represented and identify a verifiable configuration-loading path; done when custom values can be supplied without rebuilding while the default behavior remains available.

Written by the indexing model from the issue text.