Add E2E tests setup for Auto Sizes

[mukeshpanchal27]

Summary

Part of #1511

Relevant technical choices

These PR add basic infrastructure for E2E test for Auto Sizes plugin.

Run npm run test-e2e for E2E tests in local.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.48%. Comparing base (2f01c04) to head (b4758e6).
Report is 301 commits behind head on feature/1511-incorporate-layout-constraints-from-ancestors.

Additional details and impacted files

@@                                      Coverage Diff                                       @@
##           feature/1511-incorporate-layout-constraints-from-ancestors    #1988      +/-   ##
==============================================================================================
+ Coverage                                                       69.60%   72.48%   +2.87%     
==============================================================================================
  Files                                                              86       85       -1     
  Lines                                                            7018     7051      +33     
==============================================================================================
+ Hits                                                             4885     5111     +226     
+ Misses                                                           2133     1940     -193     

Flag	Coverage Δ
multisite	72.48% <ø> (+2.87%)	⬆️
single	40.43% <ø> (+0.75%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[mukeshpanchal27]

In b4758e6, I tried adding E2E tests to verify the image src before and after the plugin deactivation/activation.

When I run npm run test-e2e, it shows the same image URL (no change), but when I run npm run test-e2e:debug, it shows the expected smaller version image URL in debug mode.

Does anyone know why this might be happening or what could be causing the difference in behavior between normal and debug modes? cc. @joemcgill @felixarntz