Add local search in communities of relevant entitites

[AsphodelRem]

Add a new search engine that:

1. Retrieves the top-k most relevant entities, similarly to LocalSearchEngine.
2. Collects the communities associated with those entities, including all entities and relations contained within those communities.
3. Retrieves all source chunks from which the collected entities and relations were extracted.
4. Reranks the gathered context using either heuristic-based ranking or a reranker model, similarly to LocalSearchEngine.
5. Uses the selected context to generate the final answer to the query.