fix: update pexels link with new URL path

[brian-intel]

PR Checklist

• [x] Added label to the Pull Request for easier discoverability and search
• [x] Commit Message meets guidelines as indicated in the URL https://github.com/intel-retail/automated-self-checkout/blob/main/CONTRIBUTING.md
• [x] Every commit is a single defect fix and does not mix feature addition or changes
• [ ] Unit Tests have been added for new changes
• [ ] Updated Documentation as relevant to the changes
• [ ] All commented code has been removed
• [ ] If you've added a dependency, you've ensured license is compatible with repository license and clearly outlined the added dependency.
• [ ] PR change contains code related to security
• [ ] PR introduces changes that breaks compatibility with other modules (If YES, please provide details below)

What are you changing?

Pexels changed their URL format for downloads so new URls are required.

Issue this PR will close

close: #issue_number

Anything the reviewer should know when reviewing this PR?

Test Instructions if applicable

make run-demo

If the there are associated PRs in other repositories, please link them here (i.e. intel-retail/automated-self-checkout )