add_fact endpoint

[prasmussen15]

[!IMPORTANT] Adds add_fact method to Graphiti class for adding facts between nodes, with corresponding test and version update.

• Behavior:
  • Adds add_fact method to Graphiti class in graphiti.py to add facts between nodes.
  • Handles embedding generation for nodes and edges, resolves nodes, deduplicates edges, and adds nodes and edges in bulk.
• Testing:
  • Adds test for add_fact in test_graphiti_int.py.
  • Test creates EntityNode instances for 'Alice' and 'Bob', and an EntityEdge between them.
  • Verifies addition by performing a search and logging results.
• Misc:
  • Removes a comment about future optimization in add_episode_endpoint in graphiti.py.
  • Updates version to 0.4.0 in pyproject.toml.
  • Consistently uses timezone.utc for datetime operations across multiple files.

^{This description was created by for ac9f70acd9c358e818abd29de0fe580788b00700. It will automatically update as commits are pushed.}