Weaviate: Support for hybrid search

[bilgeyucel]

Is your feature request related to a problem? Please describe. Weaviate supports hybrid search (vector + sparse). However, Haystack doesn't support it currently.

Describe the solution you'd like To be able to control alpha parameter and other necessary configurations for hybrid search through WeaviteDocumentStore

Additional context Weaviate docs on hybrid Related issue on Weaviate repo