openai.WithEmbeddingModel option is incorrectly designating the desired model to use for embedding.

[Dmarcotrigiano]

openai.WithEmbeddingModel("text-embedding-3-large") is incorrectly returning embeddings of length 1536which is the default embedding length for models, "text-embedding-3-small" and "ada-002".
Unintuitively setting the option openai.WithModel("text-embedding-3-large") correctly returns embeddings of length 3072.

[tmc]

Fixed in #731