Doc: Create advanced MLAG upgrade example

[colinmacgiolla]

Change Summary

This is an example of creating a change control performing an upgrade on MLAG A-B pairs, with pre and post upgrade healthchecks

Related Issue(s)

N/A

Component(s) name

arista.cvp.change_control_v3

Proposed changes

Advanced playbook example

How to test

Tested against CVP 2021.2.2

Checklist

User Checklist

• N/A

Repository Checklist

• [x] My code has been rebased from devel before I start
• [x] I have read the CONTRIBUTING document.
• [x] My change requires a change to the documentation and documentation have been updated accordingly. (check the box if not applicable)
• [x] I have updated molecule CI testing accordingly. (check the box if not applicable)