Add ElasticSearchRM Class to Retrieval Modules

[Donnie]

This pull request introduces a new ElasticSearchRM class to the knowledge_storm/rm.py file. The ElasticSearchRM class allows for integration with Elasticsearch as a retrieval module, enabling the system to query and retrieve documents from an Elasticsearch index.

Changes

• Imported the Elasticsearch class from the elasticsearch package.
• Added the ElasticSearchRM class with the following features:
  • Initialization with Elasticsearch hosts and index name.
  • Method for retrieving usage statistics and resetting the counter.
  • forward method to handle search queries and return retrieved documents.

Purpose

The addition of the ElasticSearchRM class provides users with an alternative search module that leverages Elasticsearch, enhancing the flexibility and capability of the retrieval system within the STORM project.

Notes

• Ensure the elasticsearch package is installed (pip install elasticsearch) to use this new class.