Logstash benchmarks page enhancements

Tracking enhancements for the Logstash Benchmarks page here for better external consumption:
- Change from events per 2 min to EPS
- Label Y-axis of graph with EPS
- Add hardware info, just CPU and memory works
- Link to respective test config / dataset per specific graph at the bottom
- Maybe add one more config example with more filters - grok, geoip, anonymize
- Add a note at the top i.e. "The performance benchmarks here are just a baseline. The EPS may not scale linearly as hardware scales vertically. The simplicity of the stdin/stdout test configs may also yield higher EPS than real-world inputs/outputs."
- Fix performance convergence of all releases starting June 20.
- Enable underlying tool to dynamically plug in a config and test dataset for a general throughput baseline.