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

[PaulEagle97]

Hello! We have developed a custom component WeaviateHybridRetriever, based on WeaviateDocumentStore that is already used in production and we would like to know how to contribute the source code to the Open Source community of Haystack. Our implementation allows to set fusion_type, alpha and other search parameters.
I haven't found a way to directly make a pull request on this issue, could you please guide me through the process?