Add try-except to loading in the data index

[rchan26]

When running the CLI reginald_run to set up slack bot with a llama-index model, you get error when you don't have the index built (i.e. the correct folder doesn't exist in your data directory) in which case you need to build the index by using --force-new-index flag. We could have better error handling.

Either:

• Build it if you don't have it - so not necessary to --force-new-index (it'd still be useful to have because there's times where it does exist and you need to build again)
• Give better error handling to let the user know that the folder doesn't exist and need to --force-new-index

The specific lines of code to change are here:

reginald/reginald/models/models/llama_index.py

Lines 146 to 168 in 1f54b29

	if force_new_index:
	logging.info("Generating the index from scratch...")
	self._prep_documents()
	self.index = VectorStoreIndex.from_documents(
	self.documents, service_context=service_context
	)
	# save the service context and persist the index
	logging.info("Saving the index")
	self.index.storage_context.persist(
	persist_dir=self.data_dir / LLAMA_INDEX_DIR / which_index
	)
	else:
	logging.info("Loading the storage context")
	storage_context = StorageContext.from_defaults(
	persist_dir=self.data_dir / LLAMA_INDEX_DIR / which_index
	)
	logging.info("Loading the pre-processed index")
	self.index = load_index_from_storage(
	storage_context=storage_context, service_context=service_context
	)

Note: consider the folder may not exist because the data directory was misspecified, so perhaps the first suggestion is not ideal.