Instructions about alerts via SMTP and Thresholds (#498)

* Update kvm.rst - iptables before rule

On Ubuntu 24.04 LTS I found the described issue with the forwarding traffic back and fourth from guests system VMs and the physical interfaces attached to the bridges. This solved my problems.

* Update qig.rst

* Update optional_installation.rst

* Update _database.rst

* Update _database.rst

* Update qig.rst

* Update kvm.rst

* Update kvm.rst

* smtp and threshold settings

* Reordered columns or types

* clean up

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Co-authored-by: Davi Torres <[email protected]>

Author: daviftorres