sample to create a session token with a service account

[guirava]

Description

Sample script to create a session token for a given appliance with a service account,
and retrieve cluster version string from the appliance API.

Sample scripts shows 2 implementations: one using the rubrik_polaris SDK and another using a simple HTTP POST.

Related Issue

CDM-281549

https://rubrik.atlassian.net/browse/CDM-281549

Motivation and Context

With service accounts recently released,
This PR shows a simple example on how to use a service account to create a session on an appliance.

How Has This Been Tested?

manually against dev-124 GCP dev deployment with 7.0-dev cluster attached.

Types of changes

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

Go over all the following points, and put an x in all the boxes that apply. If you're unsure about any of these, don't hesitate to ask. We're here to help!

• My code follows the code style of this project.
• My change requires a change to the documentation.
• [] I have updated the documentation accordingly.
• I have read the CONTRIBUTION document.
• [] I have updated the CHANGELOG file accordingly for the version that this merge modifies.
• I have added tests to cover my changes.
• All new and existing tests passed.