chore(NA): rename journeys folder into journeys_e2e inside x-pack/performance to correctly classify journey e2e files (#178340)

The source code classifier we currently have was incorrectly classifying
e2e journey files as `non-package` instead of `tests or mocks` as it was
not using the name standards we used for FTR files.

We could have created a `functional-tests` package for the performance
folder (which is what we want to do in the future) but because we don't
have the feature to create ownerless packages it would not be easy to
find a given owner for that folder.

As such I'm just opting for a second solution which is applying the same
name standards to this journeys folder as we have for FTR and changing a
little the classifier to recognise it.

This should fix the problem found at
https://github.com/elastic/kibana/pull/178017.

Co-authored-by: Alex Szabo <alex.szabo@elastic.co>

packages/kbn-repo-source-classifier/src/config.ts

@@ -53,6 +53,7 @@ export const TEST_DIR = new Set([
   'stub',
   'e2e',
   'ftr_e2e',
+  'journeys_e2e',
   'storybook',
   '.storybook',
   'integration_tests',