We want to create a feature flag for the $rankFusion MVP and avoid doing FCV-sensitive checks so we can backport to 8.0 sooner. This MVP will be a reduced version of what's scoped under FeatureFlagSearchHybridScoringPrerequisites, but excluding

• $setWindowFields
• $geoNear
• $score
• $scoreDetails

This means that we will be including

• $rankFusion
• multiple input pipelines
• weights

This feature flag could be called simply FeatureFlagRankFusion.