Lazily build Filter in FilteredAggregatorFactory to avoid parsing exceptions in Router

[findingrish]

Query with lookups in FilteredAggregator fails with this exception in router,

Cannot construct instance of `org.apache.druid.query.aggregation.FilteredAggregatorFactory`, problem: Lookup [campaigns_lookup[campaignId][is_sold][autodsp]] not found at [Source: (org.eclipse.jetty.server.HttpInputOverHTTP); line: 1, column: 913] (through reference chain: org.apache.druid.query.groupby.GroupByQuery["aggregations"]->java.util.ArrayList[1])

The problem is that constructor of FilteredAggregatorFactory is actually validating if the lookup exists in this statement dimFilter.toFilter().
This is failing on the router, which is to be expected, because, the router isn’t assigned any lookups.
The fix is to move to a lazy initialisation of the filter object in the constructor.