Updated `search_helper_bson_obj::isMongotPipeline` function to return false for `$vectorSearch` stages which would use the extension's implementaiton.

• Modified `search_helper_bson_obj::isMongotPipeline()` to accept an `IncrementalFeatureRolloutContext` parameter and use it to check feature flags
• Refactored the function to use a helper namespace and template for cleaner stage detection
• Updated all callers of `isMongotPipeline()` to pass the `IncrementalFeatureRolloutContext`
• Updated `PipelineResolver::buildRequestWithResolvedPipeline()` to accept the IFR context