allow to specify requestConfig endpoint dynamically

## Current
the sparql endpoint is hardcoded:

```
index.html
60: requestConfig: { endpoint: 'http://odas.aau.dk/sparql' }
```

## expected
it would be nice if we could change this in an environment variable, or read from a configuration file, sot hat we can test with different sparql endpoints

Start in index.html around line 60, where requestConfig hardcodes the SPARQL endpoint. Inspect how this page is built and served before choosing between environment-based and configuration-file input. Done means different SPARQL endpoints can be selected without editing the source, and the chosen configuration path is documented.

Written by the indexing model from the issue text.