[DOCS] Add alt text to showcase homepage images

[jbampton]

Did you read the Contributor Guide?

• Yes, I have read the Contributor Rules and Contributor Development Guide

Is this PR related to a ticket?

• No:
  • this is a documentation update. The PR name follows the format [DOCS] my subject

What changes were proposed in this PR?

Key Benefits

• Ensures Accessibility: Screen readers speak alt text aloud to visually impaired visitors.
• Improves SEO: Search engines index alt text to rank images in search results.
• Provides a Fallback: Text displays if images fail to load due to slow internet.
• Ensures Legal Compliance: Meets web accessibility standards like WCAG to reduce legal risks.

How was this patch tested?

Did this PR include necessary documentation updates?

• No, this PR does not affect any public API so no need to change the documentation.