Implement cost tracking and monitoring via LiteLLM

[HamzaSardar]

• Add Postgres to docker-compose.yaml with named volume (managed by docker). Connection has a service_healthy check condition.
• Add litellm config with master key (currently placeholder) and point it to the db url.
• settings.py: add litellm_url and litellm_master_key to agensettings
• agent.py: build client with base_url pointing to the litellm anthropic endpoint, and pass it as the provider to anthropicmodel so anthropic queries pass through litellm.