Update kbn-performance-testing-dataset-extractor to read scalability setup from FTR config

[dmlemeshko]

With #132047 FTR config file can contain scalability configuration, that is required to generate scalability simulation for the single user performance journey.
During Performance WG sync @spalger suggested to pass FTR config file path to kbn-performance-testing-dataset-extractor and read scalability setup directly from it:

node scripts/extract_performance_testing_dataset 
    node scripts/extract_performance_testing_dataset \
        --config "<path to FTR config>"
        --buildId "<_source.labels.testBuildId>" \
        --es-url "<ES baseURL>" \
        --es-username "<ES username>" \
        --es-password "<ES password>"

FTR config should contain both scalabilitySetup section and journeyName in 'kbnTestServer.env['ELASTIC_APM_GLOBAL_LABELS']

output file should be updated with scalability metadata:

{
   "journeyName":"ecommerce_dashboard",
   "kibanaVersion":"8.2.0-SNAPSHOT",
   "scalabilitySetup":{
      "warmup":{
         "stages":[
            {
               "action":"constantConcurrentUsers",
               "maxUsersCount":20,
               "duration":"90s"
            }
         ]
      },
      "test":{
         "stages":[
            {
               "action":"rampConcurrentUsers",
               "minUsersCount":20,
               "maxUsersCount":100,
               "duration":"2m"
            },
            {
               "action":"constantConcurrentUsers",
               "maxUsersCount":100,
               "duration":"5m"
            }
         ]
      },
      "maxDuration":"10m"
   },
   "traceItems":[
      ...
   ]
}

[elasticmachine]

Pinging @elastic/kibana-qa (Team:QA)