[Search Sessions] Improve performance coverage

[lizozom]

During testing week, we intend to charaterize additional performance test cases.
We also want to define clearer metrics to what counts as a success \ failure.

Test cases:

• Ensure no significant impact on key metrics:
  • Response times
  • Event loop delay
  • System load
  • Disk usage
  • # of concurrent users
• Ensure running many sessions/allowing cleanup task to run doesn't leak saved objects
• Ensure saved objects aren’t persisted (or even created) if they can’t be restored
• When a session is discarded, delete saved object

[elasticmachine]

Pinging @elastic/kibana-app-services (Team:AppServices)

[lizozom]

@lukasolson @sixstringcode I wonder if we should do some quick manual testing to estimate the initial magnitude of this.
This will help us more easily determine the priority and importance of this.

[elasticmachine]

Pinging @elastic/kibana-data-discovery (Team:DataDiscovery)

[kertal]

Closing this because it's not planned to be resolved in the foreseeable future. It will be tracked in our Icebox and will be re-opened if our priorities change. Feel free to re-open if you think it should be melted sooner.