[kbn-journeys] add synthtrace support (#178599)

## Summary

Moving synthtrace clients init inside kbn-journeys:

esArchiver does not always solve the issue with data generation. We
already have afew journeys using Synthtrace instead and expect more to
come.

In order to simplify the process of creating new journeys, this PR moves
Synthtrace client initialisation into kbn-journey package and exposes a
way to define client type, generator function & its input arguments:

 ```
import { Journey, SynthtraceOptions } from '@kbn/journeys';
import { subj } from '@kbn/test-subj-selector';
import { generateApmData } from '../synthtrace_data/apm_data';

export const journey = new Journey({
  synthtrace: {
    type: 'apm',
    generator: generateApmData,
    options: {
      from: new Date(Date.now() - 1000 * 60 * 15),
      to: new Date(Date.now() + 1000 * 60 * 15),
    },
  },
})
```

PR also needs review from teams who use Synthtrace to understand if the implementation is matching expectations.

---------

Co-authored-by: kibanamachine <42973632+kibanamachine@users.noreply.github.com>

packages/kbn-performance-testing-dataset-extractor/kibana.jsonc

@@ -1,5 +1,5 @@
 {
-  "type": "shared-common",
+  "type": "test-helper",
   "id": "@kbn/performance-testing-dataset-extractor",
   "devOnly": true,
   "owner": "@elastic/kibana-performance-testing"