Description of problem:

This is a proactive note to add a Sahara warning in the future 13 to 16 FFU documentation.

Sahara is deprecated in OSP15 and support will be removed in OSP16 therefore OSP13 customers running sahara should NOT proceed with FFU.

A warning should be added to mention this before the customers actually attempt to FFU.

When https://bugzilla.redhat.com/show_bug.cgi?id=1740325 will be supported we can redirect them to the procedure to disable Sahara so that they can safely upgrade.

Worth noting that a security check will prevent customers from performing the FFU if sahara is enabled however we would prefer that customers don't start the process hence this doc BZ.
https://bugzilla.redhat.com/show_bug.cgi?id=1730322


Version-Release number of selected component (if applicable):
13 to 16 FFU

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