Support for SPARQL (#7165)

# [SPARQL](https://www.w3.org/TR/rdf-sparql-query/) for
[LangChain](https://github.com/hwchase17/langchain)

## Description
LangChain support for knowledge graphs relying on W3C standards using
RDFlib: SPARQL/ RDF(S)/ OWL with special focus on RDF \
* Works with local files, files from the web, and SPARQL endpoints
* Supports both SELECT and UPDATE queries
* Includes both a Jupyter notebook with an example and integration tests

## Contribution compared to related PRs and discussions
* [Wikibase agent](https://github.com/hwchase17/langchain/pull/2690) -
uses SPARQL, but specifically for wikibase querying
* [Cypher qa](https://github.com/hwchase17/langchain/pull/5078) - graph
DB question answering for Neo4J via Cypher
* [PR 6050](https://github.com/hwchase17/langchain/pull/6050) - tries
something similar, but does not cover UPDATE queries and supports only
RDF
* Discussions on [w3c mailing list](mailto:semantic-web@w3.org) related
to the combination of LLMs (specifically ChatGPT) and knowledge graphs

## Dependencies
* [RDFlib](https://github.com/RDFLib/rdflib)

## Tag maintainer
Graph database related to memory -> @hwchase17

pyproject.toml

@@ -114,6 +114,7 @@ openllm = {version = ">=0.1.19", optional = true}
 streamlit = {version = "^1.18.0", optional = true, python = ">=3.8.1,<3.9.7 || >3.9.7,<4.0"}
 psychicapi = {version = "^0.8.0", optional = true}
 cassio = {version = "^0.0.7", optional = true}
+rdflib = {version = "^6.3.2", optional = true}
 
 [tool.poetry.group.docs.dependencies]
 autodoc_pydantic = "^1.8.0"
@@ -310,6 +311,7 @@ all = [
     "awadb",
     "esprima",
     "octoai-sdk",
+    "rdflib",
 ]
 
 # An extra used to be able to add extended testing.