Set Up Embeddings in Default Index Settings

[alexaryn]

Is your feature request related to a problem? Please describe.
The out-of-the-box experience for Sycamore doesn't handle embeddings well. Considering that this is the main use-case, the default index settings should provide for a KNN index of embeddings.

Describe the solution you'd like
Default index settings in sycamore.writers.opensearch should be set up for embedding-based indexing and retrieval. Reasonable names should be used consistently for text, embeddings, title, author, etc.

Describe alternatives you've considered
Pass in index_settings to docset.write.opensearch(). These will be 90% copy-pasta, but have the possibility to diverge and cause problems.

Additional context
We should also revisit the integration tests to see how/if they can be simplified via defaults.

[alexaryn]

It appears that it's possible to specify index_settings at the time the index is explicitly created. It also appears possible to have the index created implicitly by simply ingesting a document. We should see if it matters which way it's done.