Specify search method

[emilradix]

Right now you have to specify whether you use hybrid, vector or keyword search in the answer_evals and rag method. If unspecified it defaults to hybrid_search.

I think this approach could lead to people accidentally mismatching their search methods, for example if they forget to specify it in answer_evals, but do in the rag method.

I think we should either force the user to always specify the search method, or have them set the default search method in the RagLiteConfig.