test(e2e): add dataset creation e2e test

[EvanYao826]

Summary

Add a new e2e test scenario for creating an empty dataset, following the existing Cucumber BDD + Playwright pattern.

Fixes #34278

Changes

• Added e2e/features/datasets/create-dataset.feature with Cucumber scenario
• Added e2e/features/step-definitions/datasets/create-dataset.steps.ts with step definitions
• Updated e2e/features/support/world.ts to track created dataset names

Test scenario

@datasets @authenticated @core
Feature: Create dataset
  Scenario: Create a new empty dataset
    Given I am signed in as the default E2E admin
    When I open the datasets page
    And I start creating a new dataset
    And I select "Create an empty dataset"
    And I enter a unique E2E dataset name
    And I confirm dataset creation
    Then I should land on the dataset document page

Checklist

• Title explains the problem clearly
• Tests added/updated (if applicable)
• Documentation updated (if applicable)
• No breaking changes