Allow ability to configure embeddings model and to re-embed all documents

[danny-avila]

Chore

New models are out would like to use text-embedding-3-small:

Model	~ Pages per dollar	Performance on MTEB eval	Max input
text-embedding-3-small	62,500	62.3%	8191
text-embedding-3-large	9,615	64.6%	8191
text-embedding-ada-002	12,500	61.0%	8191

https://platform.openai.com/docs/guides/embeddings/what-are-embeddings

Additional context

Option to re-embed documents in this case would be great. I cannot use 3-small for messages embedded by ada so would need to re-embed

[taishikato]

#79 might have solved this issue partially.