For ENG-6350, add support for rate limiting snapshots
Merge branch 'master' into ENG-6350
perf charts: flag chart with annotations if most recent measurment is out more than 5% relative to the moving avg.
For ENG-6350, for blocking snapshots, don't rate limit
Merge pull request #1390 from VoltDB/ENG-6350

Eng 6350
Merge branch 'master' of github.com:VoltDB/voltdb into ENG-6297-groupby-pk-opt