ci: run e2e tests on pull requests with an auto-generated test user

[mahdi2ba]

Description

Wires the existing WebdriverIO + Cucumber E2E suite into CI so it runs automatically on every pull request, and removes the suite's dependency on shared/hardcoded test credentials by generating a unique Keycloak user per scenario
Specifically:

• New workflow .github/workflows/treetracker-frontend-e2e-pr.yml ("E2E Tests"): starts the app, runs the suite headless in Chrome on every PR (+ manual dispatch), and uploads the Allure HTML report and the run video as a downloadable artifact.
• New helper features/support/testUser.js: registers a fresh unique user (treetracker-bdd-<timestamp>-<random>) through the Keycloak sign-up page per run,and remembers it for later steps in the same scenario.
• De-hardcoded the login, registration, change-password, update-account and organization steps to use that generated user instead of a fixed committed account.
• Un-skipped the login scenarios (they now register → log out → log back in).
• admin.feature: the one scenario needing the greenstand-admin role reads its credentials from BDD_GREENSTAND_ADMIN_USERNAME / BDD_GREENSTAND_ADMIN_PASSWORD secrets and skips cleanly when they're absent (e.g. on fork PRs).
• wdio.conf.js made CI-ready: CHROMEDRIVER_PATH / headless via env vars, safe video-capture fallback when ffmpeg is missing, and disableWebdriverStepsReporting: true so typed passwords are never written into the uploaded report.
• README.md documents the CI workflow and the env vars used.

Issue(s) addressed

• Resolves Automate E2E tests on PR with auto-generated test user (keycloak branch) #1225

What kind of change(s) does this PR introduce?

• Enhancement
• Bug fix
• Refactor

Please check if the PR fulfils these requirements

• The commit message follows our guidelines (conventional commits — ci:)
• Tests for the changes have been added (this PR is the E2E test automation itself)
• Docs have been added / updated (README CI section)

Issue

What is the current behavior?

The WebdriverIO + Cucumber E2E suite exists under features/ but is never executed in CI — the PR pipeline only runs lint, build and Jest unit tests. The suite also depends on a shared account whose username/password are hardcoded in plain text in the feature/step files, and the login/registration scenarios are disabled with @skip.

What is the new behavior?

The E2E suite runs automatically on every pull request (headless Chrome) and publishes its report + video as an artifact. Each scenario provisions its own disposable Keycloak user at runtime, so there are no shared/hardcoded credentials; the previously skipped scenarios no run. The privileged admin scenario is driven by repository secrets and skips gracefully when they aren't available.

Breaking change

Does this PR introduce a breaking change?

No. The change is additive — a new, non-blocking CI check plus test-suite refactoring.
There are no application (src/) code changes.

Other useful information

• The E2E check is intentionally informational (non-blocking) for now; it can be promoted to a required check later (note the paths filter first — see the workflow file).
• CHROMEDRIVER_PATH is set automatically in CI; local-run instructions are in the README.
• Out of scope (follow-up): removing the ~2.7 GB of committed reports/ and publishing
  the report + video to a live GitHub Pages URL are intentionally left for a separate PR.