docs: add RDF4J Store and Client user docs (#3319)

* chore: delete merged_prs.json

* docs: add rdf4j extra when building docs on readthedocs.

This is required to ensure MkDocs generate the modules correctly for the RDF4J client reference docs.

* docs: add rdf4j store docs

* chore: fix docstring reference

* docs: add rdf4j client docs

* docs: edits and refinements

* docs: convert absolute reference to relative

* docs: fix small case typo

Author: edmondchuc

.readthedocs.yaml

@@ -20,7 +20,8 @@ build:
     # the readthedocs environment.
     - pip install -r devtools/requirements-poetry.in
     post_install:
-    - poetry export --only=main --only=docs --without-hashes -o requirements.txt
+    # rdf4j extra is needed to document the modules in rdflib.contrib.rdf4j
+    - poetry export --only=main --only=docs --extras=rdf4j --without-hashes -o requirements.txt
     - pip install --no-cache-dir -r requirements.txt
     - pip install .