This sampler collects transactions generated by New Relic Synthetics up to a fixed limit and transmits their traces
at harvest time. This class does not really "sample: it behaves like a fixed-size accumulator. In order to guarantee
this behavior, however, this sampler must run at the head of the sampler search conducted by the
TransactionTraceService. Otherwise, the synthetic transaction may be "stolen" by a sampler with some
heuristic replacement behavior and then discarded before the following harvest.