Add E2E tests for Variables page (#60565)

[shashbha14]

Implements E2E tests for the Variables page as part of the UI E2E Test Scenarios meta issue.
This PR adds comprehensive end-to-end tests for the /variables page using Playwright, following the Page Object Model (POM) pattern established in PR #58548.

Changes Made

1. E2E Test Infrastructure

• Playwright Configuration (playwright.config.ts) - Multi-browser test setup
• Test Configuration (testConfig.ts) - Environment variables and settings
• Git Ignore (.gitignore) - Exclude Playwright test artifacts

2. Page Object Models

• BasePage - Common page interaction methods
• LoginPage - Authentication handling
• VariablesPage - Comprehensive Variables page interactions with 20+ methods

3. Test Specifications

• variables.spec.ts - 15 comprehensive test cases
• Complete test coverage for all Variables page features
• Automated test data creation and cleanup

4. Documentation

• README.md - Complete guide for running and writing E2E tests
• Includes setup instructions, troubleshooting, and examples

Test Coverage

✅ Variables list display
✅ Create variable (encrypted and non-encrypted)
✅ Edit variable
✅ Delete variable (single and bulk)
✅ Search variables (exact and wildcard patterns)
✅ Import variables from JSON file
✅ Pagination navigation
✅ Column sorting (key, value, description)

Testing Approach

• Framework: Playwright v1.48.2
• Pattern: Page Object Model (POM)
• Browsers: Chromium, Firefox, WebKit
• Test Data: Auto-generated with timestamps, cleaned up in afterAll
• No hardcoded values: Uses testConfig and dynamic data

How to Run

cd airflow/ui
pnpm install
pnpm exec playwright install
pnpm test:e2e

[shahar1]

Please resolve conflicts.
CC: @vatsrahul1001

[shashbha14]

Thank you for the review! The repository structure has changed since I created this branch. To avoid complex merge conflicts, I'll close this PR and create a new one based on the latest main branch.