:chore: Add steps, functions to test lazyload images -- #56

[Khadreal]

Description

Add test for lazyloading images.

Fixes #56

Documentation

The command to run npm run test:llimages

User documentation

Explain how this code impacts users.

Technical documentation

Explain how this code works. Diagram & drawings are welcomed.

Type of change

• Enhancement (non-breaking change which improves an existing functionality).

New dependencies

List any new dependencies that are required for this change.

Risks

List possible performance & security issues or risks, and explain how they have been mitigated.

Checklists

Feature validation

• I validated all the Acceptance Criteria. If possible, provide sreenshots or videos.
• I triggered all changed lines of code at least once without new errors/warnings/notices.
• I implemented built-in tests to cover the new/changed code.

Documentation

• I prepared the user documentation for the feature/enhancement and shared it in the PR or the GitHub issue.
• The user documentation covers new/changed entry points (endpoints, WP hooks, configuration files, ...).
• I prepared the technical documentation if needed, and shared it in the PR or the GitHub issue.

Code style

• I wrote self-explanatory code about what it does.
• I wrote comments to explain why it does it.
• I named variables and functions explicitely.
• I protected entry points against unexpected inputs.
• I did not introduce unecessary complexity.
• I listed the introduced external dependencies explicitely on the PR.
• I validated the repo-specific guidelines from CONTRIBUTING.md.

Observability

• I handled errors when needed.
•  I wrote user-facing messages that are understandable and provide actionable feedbacks.
• I prepared ways to observe the implemented system (logs, data, etc.).

Risks

•  I explicitely mentioned performance risks in the PR.
• I explicitely mentioned security risks in the PR.

Clicked on the approve button by mistake

[Mai-Saad]

For images with e2e domain, can we read this from env variable so it can run on any e2e env? what do you think?

[hanna-meda]

@Khadreal, I've checked all 3 scenarios. Scenario for the /ll_bg_css_double_colon template is failing because expected images no longer correspond. Left you the correct list of images in review. Thank you.