Take new OSS gatling recordings using json for Puppet 5

For Puppet 5 perf testing, we should take some new FOSS gatling recordings with an agent and server that use JSON across endpoints (instead of the legacy PSON) and have the oss-puppetserver-latest* Jenkins jobs start using them.

I think we should preserve the current recordings which use PSON as well, though, so that we can continue to run those for the oss-puppetserver-stable job for some period of time / maybe have around for Puppet 4 agent simulation posterity as may be needed.