[Edit] Problem Statement: Add Key Elements and Examples

[AnamolR]

Description

This PR updates the existing Problem Statement entry in the uiux/concepts/problem-statement section to include two new content sections: Key Elements and Example Problem Statements.

The additions provide clearer guidance on how to structure effective problem statements and illustrate real-world examples to support understanding and application concisely. These updates improve the educational value and practical utility of the entry in addition to the existing short definition.

Issues Solved

Closes #6600

Type of Change

Editing an existing entry (fixing a typo, bug, issues, etc)

Checklist

• [x] All writings are my own.
• [x] My edits follow the Codecademy Docs style guide.
• [x] My changes generate no new warnings.
• [x] I have performed a self-review of my own writing and code.
• [x] I have checked the updated content and corrected any misspellings.
• [x] I have made corresponding changes to the documentation if needed.
• [x] I have confirmed my changes are not being pushed from my forked main branch.
• [x] I have confirmed that I'm pushing from a new branch named after the changes I'm making.
• [x] I have linked any issues that are relevant to this PR in the Issues Solved section.