feat: add disaster recovery guidance for NGINXaaS for Azure deployments

[kuthiala]

Proposed changes

Adds a section for disaster recovery guidance for NGINXaaS for Azure deployments.

Testing: Describe any testing that you did.

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[github-actions]

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[mjang]

2 min review:

• It builds! see https://frontdoor-test-docs.nginx.com/previews/docs/493/nginxaas/azure/quickstart/disaster-recovery/
• You'll want to tell readers where to put the config options (I presume /etc/nginx.conf)
• I like how you've organized the titles
  • But you need some substance with the titles, to describe what you're doing -- and why you're adding code -- in each "step"

[mjang]

I haven't used NGINXaaS before, so you're welcome to ignore any/all of my comments. I am approving to expedite publishing if appropriate.

[mjang]

Retaining approval so you can publish... but I do think you need to tell users "where" to write the code samples.

[JTorreG]

approving now to make sure this is not blocked

[JTorreG]

merging this PR as per conversation in Slack.

If there is any further feedback or fixes, we will address them in a separate PR