Create custom Dockerfile extending GraphDB container

[alyssadai]

• Related to [FIX] Use jq to handle GraphDB credentials payloads with special characters #109

In order to be able to use jq to construct JSON payloads for GraphDB requests, we currently install it in the GraphDB container as part of the entrypoint script. This means that the installation happens every time the docker compose stack is re-launched, which is not super efficient.

An alternative approach would be to create a custom Dockerfile that builds on the GraphDB image, which includes jq and possibly our custom entrypoint as well. This would mean that users would use our custom GraphDB image instead of the one from ontotext.

As part of this issue, we could investigate whether the GraphDB image version should be bumped.