Forward MSAL client metadata headers through IMDS to ESTS (#902)

* Initial plan

* Add MSAL client metadata headers to IMDS managed identity requests

Add x-client-SKU, x-client-Ver, and x-ms-client-request-id headers to
_obtain_token_on_azure_vm() for IMDS token requests. Update existing
IMDS tests to assert the new headers and validate UUID correlation IDs.

Agent-Logs-Url: https://github.com/AzureAD/microsoft-authentication-library-for-python/sessions/3f0bb4c2-0e45-471e-9ab3-2a502ef8cddf

Co-authored-by: gladjohn <90415114+gladjohn@users.noreply.github.com>

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: gladjohn <90415114+gladjohn@users.noreply.github.com>