Measure performance overhead of tracing solution for Kibana server

[mshustov]

Part of #101587
Before enabling the tracing solution by default for all the Kibana instances, we should test the defaults added in #102704 do not impact the overall Kibana performance.

For testing use the standard DemoJourney from https://github.com/elastic/kibana-load-testing
Compare numbers with execution_context.enabled: true and execution_context.enabled: false.
Based on the measurements, we should decide whether we can keep execution_context.enabled: true as the default or a Kibana user should opt-in to use it.

Note that the test the overhead for server-side only. The client-side logic is small enough to neglect its influence.

[elasticmachine]

Pinging @elastic/kibana-core (Team:Core)

[LeeDr]

@dmlemeshko is this a test you could do and report the results back here? Ideally by 7.15.0 FF.

[dmlemeshko]

@LeeDr I think I should be able to run it on a Jenkins job with a small code change. I will double check with @mshustov

[dmlemeshko]

Dedicated dashboard is created to represent test results.

Test Scenario: DemoJourney
Test runs: 3 each
Branch: master (cd3cc29) vs execution-ctx-disable (mshustov@5336d3e)
Load: ramping from 20 up to 800 concurrent users

Results: avg pefromance degradation is in 17-19% range with execution_context.enabled: true in place.