Specify RankFusionSearchers via System Properties Configuration

[marevol]

We need to enhance the flexibility of our search system by allowing the specification of RankFusionSearcher through system properties. This update involves:

1. Adding a method to load searcher names from system properties.
2. Updating the RankFusionProcessor to use only the searchers specified in these properties.
3. Modifying the search logic to filter and utilize the specified searchers.

This improvement will enable more dynamic and configurable search operations.