Move default media files to regional storage

[malincrist]

Problem

The default media files are stored in a storage account from West US. VNet services can't access these files without whitelisting the endpoint and "Microsoft.Storage.Global".

Solution

Upload the media files to the regional storages that are accessible even for services in VNet and use them from there.
During provisioning, we will replace the download URL with the URL of the service and the path to the image.

Changes in the default.json file:

• re-named the files to not use GUID but the file name
• removed downloadUrl from properties
  
• changed where they are referenced to use the name not the GUID
  

[github-actions]

Accessibility Insights Action: All applicable checks passed

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