Add "auto-id" capability to Embeddings

[davidmezzetti]

Currently, an Embeddings instance requires each input to be a tuple of 3 elements, (id, data, tags). The vast majority of time, tags is empty and the id is an auto-generated number.

This change will allow the following inputs when passing data to an insert/upsert operation.

• (id, data, tags) tuples (CURRENT)
• (id, data) tuples
• data elements

In the case of just data elements, an auto id index will be used.

Note: The application interface already has similar functionality.