{Core} Enrich user-agent for az rest

[houk-ms]

Description

This PR adds more properties into az rest user-agent, making it align with the python-sdk based requests. This is suggested by our PM Arun so that we can get the python version and os info from the user agents.

Currently, a common user agent from az rest based requests could be

AZURECLI/2.11.1 (RPM)

a common user agent from python-sdk based requests could be

python/3.8.2 (Windows-10-10.0.18362-SP0) msrest/0.6.18 msrest_azure/0.6.3 azure-mgmt-resource/10.2.0 Azure-SDK-For-Python AZURECLI/2.12.1 (PIP)

The PR adds the following properties into az rest user agents:

• python-version
• os detail

These properties won't be added because they are not the dependencies of az rest.

• msrest version
• msrest_azure version

Testing Guide

Run the az rest command, e.g,

az rest --method GET --uri 'https://graph.microsoft.com/v1.0/applications/b4e4d2ab-e2cb-45d5-a31a-98eb3f364001' --debug

Previously, the userAgent is

AZURECLI/2.12.1 (PIP)

Now, the userAgent is

python/3.8.2 (Windows-10-10.0.18362-SP0) AZURECLI/2.12.1 (PIP)

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[houk-ms]

An exmaple of the az rest UserAgent now: python/3.8.2 (Windows-10-10.0.18362-SP0) AZURECLI/2.12.1 (PIP)