[performance testing] Setup isolated user journey tests

[spalger]

We need to create a small number of tests that run through specific user journeys in Kibana. These tests might be written using @elastic/synthetics, though some testing should be done to make sure that's a good idea. Synthetics run using Playwright, which is a lower level browser automation and testing tool than we use in our current FTR tests. Unlike other new testing tools, Playwright maintains an API similar to what we get with selenium-webdriver so we should be able to adapt our existing services to work with it. Playwright is also much faster than selenium-webdriver, implying to me that we should be able to get more reliable data from it WRT performance.

When running these tests Kibana should be shipping APM data to ES at a 100% sample rate with spans and transactions labeled so that we can investigate the transactions and spans created in a specific PR or Kibana CI build.

[elasticmachine]

Pinging @elastic/kibana-operations (Team:Operations)