Docs: update Pages illustrations

What does this MR do?

MVC for better illustrating Pages:

• Replace table of illustrations (optimized for mobile devices) with single illustration (optimized for /help).
• Introduce new illustration for getting started section.

Review app: http://docs-preview-ee-19585.178.62.207.141.xip.io/ee/user/project/pages/index.html

Related issues

• Follow-up from !19436 (merged)
• Related to #30647 (closed), #31712 (closed)
• Closes #34710 (closed)

Author's checklist

• Follow the Documentation Guidelines and Style Guide.
• If applicable, update the permissions table.
• Link docs to and from the higher-level index page, plus other related docs where helpful.
• Apply the documentation label.

Review checklist

All reviewers can help ensure accuracy, clarity, completeness, and adherence to the Documentation Guidelines and Style Guide.

1. Primary Reviewer

• Review by a code reviewer or other selected colleague to confirm accuracy, clarity, and completeness. This can be skipped for minor fixes without substantive content changes.

2. Technical Writer

• Optional: Technical writer review. If not requested for this MR, must be scheduled post-merge. To request for this MR, assign the writer listed for the applicable DevOps stage.

3. Maintainer

1. Review by assigned maintainer, who can always request/require the above reviews. Maintainer's review can occur before or after a technical writer review.
2. Ensure a release milestone is set and that you merge the equivalent EE MR before the CE MR if both exist.
3. If there has not been a technical writer review, create an issue for one using the Doc Review template.