Add User-Agent string to identity psresourceget in telemetry

[adityapatwardhan]

PR Summary

Add User-Agent header to ACR calls so we can get telemetry for usage

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[adityapatwardhan]

Closing this PR as the useragent string is already being added via constructor:

https://github.com/PowerShell/PSResourceGet/blob/f1b3cf7af01eab5ef2e5b3cef7b910a4a4b1e7b4/src/code/ACRServerAPICalls.cs#L63-L64