Adopt Marketplace CDN changes

[joaomoreno]

• Support redirection in Marketplace requests
• Support gzip encoding in Marketplace requests
• Include the default icon in the product
• Add "assetTypes":["Microsoft.VisualStudio.Services.Icons.Default"] and flag 0x02 to be able to figure out whether an extension has an icon
• Only request for the latest extension version during a query
• Don't interpolate asset URLs, request them all
• Send redirect=true when fetching the extension VSIX. In case of error, fallback to a request without that parameter.
• Implement CDN fallback logic, with telemetry
• Add telemetry for asset download time