Is it possible to create a string metric with set semantics? Something like an HLL sketch but being able to pull the actual string values stored? I could set a string dimension field but for performance reasons I would rather just append to the set and pull the entire aggregated set in a single row. In my use case the string I want to add has a high cardinality (>1 million) and the number of rows (and segments) would explode if I added it as a dimension.