Support cohere embeddings

**Add support for Cohere embeddings**

- Create datasets for Huggingface
- Update vectordb scanner to use Cohere as custom embedding function
- Update config parser to load Cohere model choice and API key

```
import cohere
co = cohere.Client(API_KEY)
response = co.embed(
  model='embed-english-v2.0',
  texts=[""])
print('Embeddings: {}'.format(response.embeddings))
```