An Config option to simply allow nested VM access

### The required feature described as a wish

As asked in this discusssion: https://github.com/apache/cloudstack/discussions/10225

I would like to have an easier way to allow network traffic to nested VM's in basic networking installations.

Currently you would need to manually "hack" the `security_group.py` script to just not execute anything at all.
This would be useful for inhouse non security sensitive installation where people could simply host e.g. test CloudStack installations
or other virtualization platforms to test.

Start with the linked discussion and the security_group.py script to understand the requested behavior and current traffic handling. Define how a configuration option should allow nested VM traffic in basic networking without modifying the script, then verify the option works for the described test CloudStack setup.

Written by the indexing model from the issue text.