Generate scalability tests based on single user benchmarking build artifacts

[dmlemeshko]

In elastic/kibana#130777 we pull APM traces collected during single user benchmarking journeys run on CI job and normalise into format representing a sequence of Kibana API calls: each journey has its own json files stored as artifact of that CI job.

We need to change current scalability benchmarking job to do the following:

1. Pull artifacts from the latest single user benchmarking job build

• we can use buildkite API to get the latest build and fetch artifacts, or try accessing artifacts directly?
• to use buildkite API we need an API token
• we will use public bucket to store Kibana build, plugins and jsons with API calls

2. Generate Gatling simulations using scalability-simulation-generator :

• node scripts/generate_simulations.js --dir <path to json files> --packageName org.kibanaLoadTest --url <kibana baseUrl>

3. Download (or build fresh based on commit hash) Kibana build used by single user benchmarking job

• we can probably start with fresh build based on commit hash of the buildkite build

5. Build this project with generated simulations inside and run scalability tests

• copy generated scala files under src/test/scala/org/kibanaLoadTest/simulation
• build project mvn clean test-compile
• run test gatling:test -Dgatling.simulationClass=org.kibanaLoadTest.simulation.<generated_simulation_file_name>

[dmlemeshko]

It was implemented in #272 and #279

Simulations files are not generated, instead Gatling reads json file from scalability-simulation-generator and creates simulation scenario in runtime:

mvn gatling:test -Dgatling.simulationClass=org.kibanaLoadTest.simulation.generic.GenericJourney -DjourneyPath=<path to json file> -DKIBANA_HOST=<Kibana host url>