Azure: Add telemetry for poll IMDS

[johnsonshi]

Proposed Commit Message

Azure: Add telemetry for poll IMDS

Additional Context

_poll_imds within DataSourceAzure.py currently doesn't have the Azure telemetry decorator @azure_ds_telemetry_reporter. This decorator enriches telemetry needed for diagnosing issues related to Azure polling of IMDS.

Test Steps

• Deployed a Canonical:UbuntuServer:18.04-LTS:latest VM on Azure.
• Built a deb package out of my branch's cloud-init.
• Installed the deb in the Azure VM.
• Cleaned the VM and captured it into a generalized custom image.
• Deployed and provisioned a VM from this generalized custom image containing custom cloud-init.
• Verified that everything works.

Checklist:

• My code follows the process laid out in the documentation
• I have updated or added any unit tests accordingly
• I have updated or added any documentation accordingly

[OddBloke]

Thanks!