Embedding functions

[BlackyDrum]

Added

• CohereEmbeddingFunction: Added new embedding function for Cohere.
• VoyageAIEmbeddingFunction: Added new embedding function for VoyageAI.
• TogetherAIEmbeddingFunction: Added new embedding function for TogetherAI.
• Custom Exceptions for Embedding Provider Request failures: Introduced specific exceptions to handle embedding provider request failures.
• dimension parameter for OpenAI Embedding models: Added support for specifying the dimension parameter for third generation OpenAI embedding models.

Fixed

• Readme namespace: Corrected namespace references in the Readme documentation.
• Character set for embedding requests: Fixed issues with character set handling in embedding requests.