add custom builder for VectorsConfig

[generall]

Allows to create vector configs like this:

        let mut vector_config = VectorsConfigBuilder::default();

        vector_config.add_named_vector_params(
            "large_vector",
            VectorParamsBuilder::new(8, Distance::Cosine),
        );
        vector_config.add_named_vector_params(
            "small_vector",
            VectorParamsBuilder::new(4, Distance::Euclid),
        );

        let create_collection =
            CreateCollectionBuilder::new(collection_name).vectors_config(vector_config);

[JojiiOfficial]

Not sure if add is the right prefix here. It sounds to me as if you can call it multiple times. What do you think about naming it with_vector_params or just vector_params as the other setter functions?

[generall]

then it won't be consistent with add_named_vector_params (which is not setter), because it won't overwrite data there with non-default name

[JojiiOfficial]

I'm not sure whether it needs to be treated that similar to add_named_vector_params because one is basically a setter and one not.
It was just a suggestion because I can imagine user getting confused by this. With the comment I think it'd be fine either way so feel free to mark this as resolved