Add Huggingface embeddings and Cohere embeddings (#63)

* Add huggingface embeddings and cohere embeddings
* Update openai interface and the mock for newer OpenAI SDK

---------

Co-authored-by: trducng <trungduc1992@gmail.com>

knowledgehub/embeddings/cohere.py

@@ -0,0 +1,12 @@
+from langchain.embeddings import CohereEmbeddings as LCCohereEmbeddings
+
+from kotaemon.embeddings.base import LangchainEmbeddings
+
+
+class CohereEmbdeddings(LangchainEmbeddings):
+    """Cohere embeddings.
+
+    This class wraps around the Langchain CohereEmbeddings class.
+    """
+
+    _lc_class = LCCohereEmbeddings

knowledgehub/embeddings/huggingface.py

@@ -0,0 +1,12 @@
+from langchain.embeddings import HuggingFaceBgeEmbeddings as LCHuggingFaceEmbeddings
+
+from kotaemon.embeddings.base import LangchainEmbeddings
+
+
+class HuggingFaceEmbeddings(LangchainEmbeddings):
+    """HuggingFace embeddings
+
+    This class wraps around the Langchain HuggingFaceEmbeddings class
+    """
+
+    _lc_class = LCHuggingFaceEmbeddings