Update MediaPlayerElement.md sample url

[patnels]

Update sample url to the new asset server

What changes to the docs does this PR provide?

We are retiring the mediaplatstorage1 server. Updating the url to the new sample asset server.

PR Checklist

Please check if your PR fulfills the following requirements:

• Correctly picked the right branch to base the change off (dev for new features, main for typos/improvements)
• For new pages, used the provided template
• For new features, added an entry in the Table of Contents
• Ran against a spell and grammar checker
• Contains NO breaking changes

[learn-build-service-prod]

Learn Build status updates of commit 6354b8b:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/controls/wpf-winforms/MediaPlayerElement.md	✅Succeeded	View

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