🔧 chore(__main__.py): update cache and database environment variable names for clarity and consistency

The `cache` option has been changed to use the `LANGFLOW_LANGCHAIN_CACHE` environment variable instead of `LANGCHAIN_CACHE` for clarity and consistency. Similarly, the `database_url` option now uses the `LANGFLOW_DATABASE_URL` environment variable instead of the previous behavior of using a local SQLite database by default. This change allows for more flexibility in configuring the cache and database connections.