Stored conversation history by appending prompts and responses
to self.converser_cog's instance of full_conversation_history.
The logic for ShareView and ShareButton is exactly the same as index
text_service_cog.py. The view is sent along with the link to the
sandbox in code_interpreter_service_cog, however.

Made a new instance variable in index_service_cog.py,
full_conversation_history (similar to the one in text_service_cog.py)
Adds all index chat prompts and responses to full_conversation_history.
Changed the end/stop conversation handler to index_service_cog.py from
index_model.py. Sends the ShareView when it detects the end/stop,
same as in text_service_cog.py and code_interpreter_service_cog.py.

Typecasted Response object to string so that it could be serialized
into JSON and sent to ShareGPT.