Add details on outbound SNAT

[wilfriedwoivre]

Add the IANA RFC 6598 on the FAQ as indicate on the specific page https://learn.microsoft.com/en-us/azure/firewall/snat-private-range?WT.mc_id=AZ-MVP-4039694

[prmerger-automator]

@wilfriedwoivre : Thanks for your contribution! The author(s) have been notified to review your proposed change.

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Learn Build status updates of commit d3bad46:

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[prmerger-automator]

PRMerger Results

Issue	Description
Yaml File(s)	This PR includes changes to .yml file(s) owned by another author.

[Jak-MS]

@vhorne
Can you review the proposed changes?

Important: When the changes are ready for publication, adding a #sign-off comment is the best way to signal that the PR is ready for the review team to merge.

#label:"aq-pr-triaged"
@MicrosoftDocs/public-repo-pr-review-team

[vhorne]

#sign-off

[wilfriedwoivre]

@vhorne Thanks for your review, can you approve or reject the change.