JSON loader (#4067)

This implements a loader of text passages in JSON format. The `jq`
syntax is used to define a schema for accessing the relevant contents
from the JSON file. This requires dependency on the `jq` package:
https://pypi.org/project/jq/.

---------

Signed-off-by: Aivin V. Solatorio <avsolatorio@gmail.com>

tests/integration_tests/document_loaders/test_json_loader.py

@@ -0,0 +1,16 @@
+from pathlib import Path
+
+from langchain.document_loaders import JSONLoader
+
+
+def test_json_loader() -> None:
+    """Test unstructured loader."""
+    file_path = Path(__file__).parent.parent / "examples/example.json"
+    loader = JSONLoader(str(file_path), ".messages[].content")
+    docs = loader.load()
+
+    # Check that the correct number of documents are loaded.
+    assert len(docs) == 3
+
+    # Make sure that None content are converted to empty strings.
+    assert docs[-1].page_content == ""

tests/integration_tests/examples/example.json

@@ -0,0 +1,25 @@
+{
+    "messages": [
+        {
+            "sender_name": "User 2",
+            "timestamp_ms": 1675597571851,
+            "content": "Bye!"
+        },
+        {
+            "sender_name": "User 1",
+            "timestamp_ms": 1675597435669,
+            "content": "Oh no worries! Bye"
+        },
+        {
+            "sender_name": "User 2",
+            "timestamp_ms": 1675595060730,
+            "photos": [
+                {
+                    "uri": "url_of_some_picture.jpg",
+                    "creation_timestamp": 1675595059
+                }
+            ]
+        }
+    ],
+    "title": "User 1 and User 2 chat"
+}