attestation crate - Attempt to use Azure instance metadata service during attestation type detection.

[ameba23]

During attestation type detection we establish whether we are on Azure by attempting an Azure vTPM attestation which internally hits the IMDS service which is only provided by Azure.

A nicer initial check would be to use their metadata API as documented here:

https://learn.microsoft.com/en-us/azure/virtual-machines/instance-metadata-service?tabs=linux

For context see #1 (comment)