Create Langchain LLM converter to quickly supply it to Langchain's chain (#102)

* Create Langchain LLM converter to quickly supply it to Langchain's chain

* Clean up

knowledgehub/llms/completions/base.py

@@ -1,5 +1,5 @@
-from kotaemon.base import BaseComponent
+from kotaemon.llms.base import BaseLLM
 
 
-class LLM(BaseComponent):
+class LLM(BaseLLM):
     pass