[Multi-User Part 3]: Separate chat sesssions based on authenticated users (#511)

- Add a data model which allows us to store Conversations with users. This does a minimal lift over the current setup, where the underlying data is stored in a JSON file. This maintains parity with that configuration.
- There does _seem_ to be some regression in chat quality, which is most likely attributable to search results.

This will help us with #275. It should become much easier to maintain multiple Conversations in a given table in the backend now. We will have to do some thinking on the UI.

tests/test_client.py

@@ -119,7 +119,12 @@ def test_get_configured_types_via_api(client, sample_org_data):
 def test_get_api_config_types(client, search_config: SearchConfig, sample_org_data, default_user2: KhojUser):
     # Arrange
     text_search.setup(OrgToJsonl, sample_org_data, regenerate=False, user=default_user2)
+
+    # Act
     response = client.get(f"/api/config/types")
+
+    # Assert
+    assert response.status_code == 200
     assert response.json() == ["all", "org", "image"]