Add s-nail package

Dimitra Chatzichrysourequested to merge
fix-mail into master

Mailx which is used to send emails with smtp is missing from the el9 image.
Related ticket: https://cern.service-now.com/nav_to.do?uri=incident.do?sysparm_query=number=INC3659926

Edited by Dimitra Chatzichrysou

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